Abstract: The characteristics of ultramicroscopic organic lithology of excellent marine shale were investigated by means of whole rock X-ray diffraction and Scanning Electron Microscopy(SEM) equipped with Energy Dispersive Spectrometer(EDS).Excellent marine shales consisted mainly of quartz and calcareous mineral(calcite),the content of clay minerals such as illite and montmorillonite was commonly lower than 20% and the average was only about 5%.The total organic carbon content(TOC) had a positive correlation with the quartz content but a negative correlation with clay minerals content.Excellent marine shales in the Upper Permian sequence of inner-platform sag in northeastern Sichuan Basin chiefly composed of silicesous mineral(quartz) and calcareous mineral,but contained almost no clay.The siliceous minerals and calcareous minerals in excellent marine shale were organic origin because that they were developed originally from the siliceous bioclastic of hydrocarbon generation orga-nism experienced diagenesis.Almost ultramicroscopic particles of the siliceous bioclastic contained orga-nic carbon and sulfur,and there were a positive correlation between the contents of carbon and sulfur.Inner platform sag sedimentary environment was favorable for deposition of shale with high TOC and silices mineral but low clay contents.