The paper presents organic petrological and geochemical studies of Triassic source rocks in the Tarim Basin. A particular source rock was found, which mainly consisted of biodegraded amorphinite or its thermally altered product micrinite B. This source rock was characterized not only by obvious suppression of measured vitrinite reflectance, but early hydrocarbon generation. The rock had an oil window in the range of vitrinite reflectance 0.40-0.95% and was found to have attained mature to oil peak stages in most part of the Lunnan area and Manjiaer Depression. This study has given same new evidence for a re-evaluation of hydrocarbon potential of Triassic source rocks in the Tarim Basin.