Although the original religion of the Khitan was a veneration of numerous natural appearing that were thought to represent and inheriting deity, and above all the sun, Buddhism (Fojiao 佛教) soon penetrated the society of the Khitan realm, especially after the conquest of the Bohai empire 渤海 and the increasing number of Chinese that lived in the Liaodong area 遼東 (called Yan-Yun 燕雲, modern Liaoning).
In far antiquity, a white horse and a grey ox were the venerated representatives of the Khitan tribes, and served as symbols of two tribes that were linked through intermarriage, like the imperial clan of the Yelü 耶律 and the clan of the Xiao 蕭 that produced most of the Khitan empresses. Before military campaigns, horse and ox were sacrified to the heaven, and a shaman made an oracle of the bones of a white sheep. The most important offering rites of the Khitan rulers were offerings for Heaven and Earth (jishanyi 祭山儀), offerings for the evocation of rain (seseyi 瑟瑟儀), offerings of tribal chieftains (chaiceyi 柴冊儀), offerings for the deceased rulers (ruojieyi 爇節儀), and offerings at the end of the year (suichuyi 歲除儀).
Like through all ages and regions, the construction activity of Buddhist monks took place in the Liao empire, and many househould were liable of taxation not to the state but also the monasteries (double-tax households, ershui hu 二稅戶) that shared their tax income with the state. The most important Buddhist sect of the Liao empire was the Huayan Sect (Huayanzong 華嚴宗) with its center at the Wutaishan 五台山 near Datong 大同/Shanxi, less important was Tantrism (Mizong 密宗). Four great sutras were incised into stone slabs during the reign of Emperor Xingzong 遼興宗: The Prajnaparatima Sutra (Da banruo jing 大般若經), the Dabao jijing 大寶積經, the Nirvana Sutra (Niepanjing 涅槃經), and the Garland Sutra (Huayanjing 華嚴經). At the same time, a Buddhist canon was compiled, commented, and printed by woodblocks, Dazangjing 大藏經, later a second edition called Khitan Canon (Danzang 丹藏). The most important book compiled by a Buddhist monk of the Liao period is the Longkan shoujing 龍龕手鏡 (later shoujian 手鑒) "Hand mirror for the dragon niche", written by Xingjun 行均, a dictionary that reflects the popular characters, writing style, and pronunciation of more than 26,000 Chinese characters. The preserved Liao period Buddhist buildings are the main hall of the Dule Monastery 獨樂寺 in Jixian 薊縣/Tianjin, the brick stupa of Tianning Monastery 天寧寺/Beijing, the pagoda in Ningcheng 寧城 (modern Chaoyang 朝陽/Liaoning), and the Wooden Stupa of Yingxian 應縣/Shanxi. All these stupas were octogonal and did not have a hollow interior. This was a new architectural style that was typically for the Liao and Jin periods, while other Liao stupas like the white brick stupa of Linxi 林西 (near Chifeng 赤峰/Inner Mongolia) had a hollow interior until the top storey.
The veneration of mountains (jishan 祭山, baishan li 拜山禮) belonged to the auspicious rites (jili 吉儀, see five rites) of the Khitan Liao dynasty. The rites mainly concerned Mt. Muye 木葉山 (at the confluence of River Šira Mören and the Laoha 老哈) and were, according to legend, created by Hula Qaghan 胡剌可汗 from the Yaonian tribe 遙輦 (fl. 746). During the ceremony, a tablet was built, directed towards the east to face the spirits of Heaven and the earth. Before the tablet, two rows of trees were planted signifying the courtiers and nobles. The most distant trees signified the gates for the spirits (shenmen shu 神門樹). When the emperor and his consort arrived on their horses, the courtiers and court ladies took their positions in two rows. Members of different tribes wore robes with different colours. sacrificial animals were slaughtered and their members hang up on the trees. Shamans (wushi 巫師) then spread wine over the flesh. In the end, the emperor ordered the male members of the imperial clan to proceed three times around the gate trees, while all others surrounded them seven times. Emperor Taizong 遼太宗 once visited Youzhou (today’s Beijing) and took the statue of Boddhisattva Guanyin 觀音 out of the Dabei Hall (Dabei ge 大悲閣) and had it brought to Mt. Muye. He had built a temple ontop, where he venerated his ancestral spirits. From then on, all courtiers and participants of the ceremony had to wear white clothes as the deity Guanyin. The clothes and caps were again changed during the reign of Emperor Xingzong.