Investigations have been canrried out to determine the compositional changes of organic matter in Miocene Josoji black mudstones affected by igneous intrusion,and also by artificial heating.We collected mudstone samples from three outcrops in Shimane Peninsula where the mudstones had been intruded by rhyolite and andesite magma.Organic matter in the mudstones decreased from about 0.6% to 0.01% in TOC content with decreasing distance to the contact plane.Heating experiments at 600℃ for 2 days decreased TOC content from 0.65% to 0.29%.n-Alkanes and biomarkers were detected even at the contact plane,and in the 600℃ heating products.CPI increased and Pr/Ph ratio decreased with increasing temperature.