I'm not convinced either way on this issue..here are some teachings I got from a site that is against gambling
Council of Elvira, Canon 79 (A.D. 306): “Christians who play dice for money are to be excluded from receiving communion. If they amend their ways and cease, they may receive communion after one year.”
Apostolic Constitutions of the Holy Apostles, Canon 42: “Let a bishop, or presbyter, or deacon who indulges himself in dice or drinking, either leave off those practices, or let him be deprived.” Canon 43: “If a sub-deacon, a reader, or a singer does the like, either let him leave off, or let him be suspended; and so for one of the laity.” (The Apostolic Constitutions, Treatises on Early Christian Discipline)
St. Thomas Aquinas (1225-1274 A.D.), who is regarded as one of the most important Doctors of the Church, writes the following concerning the above two canons: “We read in the Canons of the apostles (Can. xli, xlii): ‘A bishop, priest or deacon who is given to drunkenness or gambling, or incites others thereto, must either cease or be deposed; a subdeacon, reader or precentor who does these things must either give them up or be excommunicated; the same applies to the laity.’ Now such punishments are not inflicted save for mortal sins. Therefore drunkenness [and gambling] is a mortal sin.” (St. Thomas Aquinas, Summa Theologica, Second Part of the Second Part, Q. 150, A. II. Whether drunkenness is a mortal sin?)
St. Clement of Alexandria, echoing the Church’s constant tradition from the beginning against gambling, and the pursuit of gain caused by the evil desire for riches “apart from the truth”, wrote in the second century A.D.: “The game of dice is to be prohibited, and the pursuit of gain, especially by dicing [and other such games of gambling], which many keenly follow. Such things the prodigality of luxury invents for the idle. For the cause is idleness, and a love for frivolities apart from the truth. For it is not possible otherwise to obtain enjoyment without injury; and each man’s preference of a mode of life is a counterpart of his disposition.” (Ante-Nicene Fathers, Vol 2, p. 485)
The venerated Dominican friar and preacher Girolamo Savonarola (1452-1498) expounds on gambling and related activities at some length, but more frequently inveighs against the corrupt manners of the age, denouncing in turn every vice that was then prevalent. This, for instance, is how he speaks against gambling: “If you see persons engaged in gambling in these days, believe them to be no Christians, since they are worse than infidels, are ministers of the evil one, and celebrate his rites. They are avaricious men, blasphemers, slanderers, detractors of others’ fame, fault-finders, they are hateful to God, are thieves, murderers, and full of all iniquity. I cannot permit ye to share in these amusements; ye must be steadfast in prayer, continually rendering thanks to the Almighty in the name of our Lord Jesus Christ. He that gambles shall be accursed, and accursed he that suffers others to gamble; shun ye their conversation, for the father that gambles before his son shall be accursed, and accursed the mother that gambles in her daughter’s presence. Therefore, whoever thou art, thou shalt be accursed if thou dost gamble or allow others to gamble;” (Life and Times of Girolamo Savonarola, chapter VIII, p. 105)
The Catholic Encyclopedia adds that: “From very early times gambling was forbidden by canon law. Two of the oldest (41, 42) among the so-called canons of the Apostles forbade games of chance under pain of excommunication to clergy and laity alike. The 79th canon of the Council of Elvira (306) decreed that one of the faithful who had been guilty of gambling might be, on amendment, restored to communion after the lapse of a year. A homily (the famous "De Aleatoribus") long ascribed by St. Cyprian, but by modern scholars variously attributed to Popes Victor I, Callistus I, and Melchiades, and which undoubtedly is a very early and interesting monument of Christian antiquity, is a vigorous denunciation of gambling. The Fourth Lateran Council (1215), by a decree subsequently inserted in the "Corpus Juris", forbade clerics to play or to be present at games of chance. Some authorities, such as Aubespine, have attempted to explain the severity of the ancient canons against gambling by supposing that idolatry was often connected with it in practice. The pieces that were played with were small-sized idols, or images of the gods, which were invoked by the players for good luck. However, as Benedict XIV remarks, this can hardly be true, as in that case the penalties would have been still more severe.” [Notice how a modernistic scholar tried to explain away the ancient Church teaching against gambling. However, this false theory of him (and of others like him) was of course refuted by Pope Benedict XIV]. (The Catholic Encyclopedia, Vol. 6, "Gambling", A.D. 1909)