This thesis, The purpose of the study, three factors:

(1)     To study a Buddhist  Holy day in Theravada Buddhism

(2)     To study the practical principles of the Buddhist Holy day in Theravada Buddhism, and

(3)   To  study procedure in Buddhist Holy day of the Buddhists in the present Thai society. The results showed that

         The Background of Buddhist Holy day in the Theravada Buddhism found that in the Buddhist era. The king Bhimbhisara who ruled Bihar, He met the Buddha where stands at Griddhakuta hill near the city of Rajgri, the capital of Magadha, The king said substance that Priests in other religions have the discussion about the teaching of religious principles. But Buddhist religion is not. Buddha allowed the monks to discuss the teaching of Buddha and a sermon to the people along the application of King Bhimbhisara.

         Ever since the day of the eighth lunar day, the fifteenth lunar day night (full moon day), the eighth waning day and the fifteenth waning day  (if any month is lunar month with only ๒๙ day to be considered as the fifteenth waning days).

                         The Buddhist Holy day   in the activities of present Thai Buddhist  found that : (1)

On the Buddhist Holy day  in a part of Thai Buddhists go to make merit in the monastery  and the other part is to pray and respect that at home, or even a priest and a novice in the same activities. If you consider the Buddhist Holy day in the present Thai society, in the morning of the Thai Buddhists to make merit, offer food, received precepts, and listen sermons and main precepts. This reflects the faith and the belief that the Buddhist Holy day. Thai society has been long practice that is important to listen to the sermons of the Thai monks at the monastery. Thailand is evidence that the tradition dates from the Sukhothai period and in the present. To maintain Buddhism and will continue to the post.