The geochemical properties of shale were studied in the Assam-Arakan basin covering a portion of the Tirap district of Arunachal Pradesh. Here the dominant rock type is light to dark grey shale belonging to the Disang Group of Eocene age. The northeast-southwest trending shale of Disang Group exposed in Tisa river and Deomali-Longding road section showing distinct fissility parallel to the bedding plane. Grey to dark grey and fine-grained sandstone, which is either massive or thin bedded, occurs interbedded with shale. The Rock-Eval analysis of shale samples from the outcrops shows high Tmax values and lower TOC and S2 values. Thus, it transpires that source-rating of studied shale, is found to be poor and also its source proclivity is towards gas. Further, shale of Disang Group is found to contain over-matured organic matters, represented by Kerogen Type-III and Type-IV.