This paper deals with the indigenous religion and culture of the Thengal Kachari tribe of Assam. The Thengal Kachari tribe is an indigenous and major type of ethnic group of Assam. The tribe lives basically in upper Assam. The traditional ritual and practices of the Thengal Kachari include ‘Deoban’ or ‘Habi puja’, Batbon Puja and so on. The Thengal Kachari tribe believes in Hinduism. They celebrate the festival called 'Tora Chira'. The Thengal Kacharis are belonging to the Indo-Mongoloid race with mythical ancestry. They are a clan of the Bodo- Kachari ethnic group. They are one of the ancient inhabitants of Assam and have a rich cultural heritage. They have adopted other cultures and as a result, they even lost their dialect and adopted Assamese as their language. But at the same time, the community is trying to maintain its traditional customs. This paper tries to reflect the traditional religion and culture of the Thengal Kacharis and their changes in the Jorhat district of Assam. The study is mainly conducted in the area of Borholla, Jorhat district of Assam. In this study, we have chosen two villages, namely- Balijan2no block gaon and Thengal Kacharigaon. Two village headmen, 40 educated persons (twenty each) from two villages, and a few (10) prominent leaders of the tribe are chosen as the respondent of the study by using the purposive sampling method. For the collection of the data, we have used both primary and secondary sources.