Bulk organic carbon isotope compositions and the abundance of acritachs, algae and microbes were examined from the Permian—Triassic boundary at Xinmin section, Guizhou. δ13Corg 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 shallowwater sections, indicating deteriorating ecological environment, low marine productivity and delayed biological recovery.