Abstract:Bulk organic carbon isotope compositions and the abundance of acritachs, algae and microbes were examined from the Permian—Triassic boundary at Xinmin section, Guizhou. δ13Corg data highlight environment changes in the latest Permian and show the following features: a gradual decreasing phase begins in Clarkina yini zone, corresponding to the low abundance value of acritachs, algae and microbes; a sharp decreasing phase occurs during Clarkina meishanensis zone, which could be caused by the combination of volcanic activity, marine biological breakdown and a sudden release of methane hydrate. The two phases reflect that the marine environment changed from the gradual transformation to mutation process. δ13Corg exhibit a positive peak before the sharp decrease above the event horizon, and the flourishing of green sulfur bacteria may result in this positive peak. δ13Corg in Xinmin section is still a downward trend in the earliest Triassic compared with some shallowwater sections, indicating deteriorating ecological environment, low marine productivity and delayed biological recovery.