Abstract: Ar-ion beam scanning electron microscope (SEM) imaging and the quantitative analysis of pore types were performed on 7 shale samples from the Longmaxi Formation in the eastern Sichuan Basin to define the vertical distribution characteristics of pore types in various lithofacies of shale. Five regions were selected in each sample to accommodate the heterogeneity of the shales, and each region (100 μm×100 μm) was analyzed using 100 SEM photographs which were magnified 14 000×. A 2000 point-count method was employed to count the plane porosity of various pores on each SEM photograph, and then the average percentage of various pores in each sample was obtained. The results showed that interparticle (interP) pores, intraparticle (intraP) pores and organic matter (OM) pores could be observed in the study area, and the contents of various pore types were different in various lithofacies. The lithofacies of Longmaxi Formation changed from argillaceous shale, silty shale to siliceous shale from top to bottom. The main pore type changed from intraP pores to OM pores with the increase of TOC content and the decrease of clay content. The content of brittle minerals controlled the quantity of interP pores, clay content controlled the development degree of intraP pores, while TOC and authigenic quartz contents determined the quantity of OM pores. Siliceous shale in the lower segment of Longmaxi Formation is the most favorable reservoir for shale gas.