Widely distributed in the Middle Yangtze Platform, Lorigniaxi, Dalong and Dongyuemiao shales are the most potential target zones for shale gas development in south China. In this study, samples from these main shale gas-producing intervals, with a range of total organic carbon (TOC), mineral compositions, and thermal :maturities (from mature to overmature), were selected from three shale gas wells in the Middle Yangtze Platform to investigate their pore structures and spontaneous imbibition characteristics. Mercury injection capillary pressure (MICP) results show the pore throats in these organic shales are mainly within nanometer range, and the pores with pore-throat diameter of 3-50 nm account for 56.7%-73.1% of the total pore volume in mature Dongyuemiao Shale, which is comparative to S1.4%-82.7% for Dalong Shale but smaller than the 68.1%-86.5% range for overmature Longmaxi Shale, which is probably associated with abundance of organic matter-hosted pores in Longmaxi Shale. According to the different imbibition behaviors toward deionized (DI) water (a hydrophilic fluid) and n-decane (a hydrophobic fluid), the pore connectivity and wettability characteristics were qualitatively assessed. Most of the shales exhibit a better pore connectivity toward n-decane, while a few samples with high brittle minerals and clay minerals contents have a high imbibition rate for DI water. Imbibition tests also suggest that Longmaxi Shale is mixed-wet, while Dalong and Dongyuemiao Shales are oil-wet or weakly water-wet, which is generally consistent with the contact angle measurement. Sorptivity obtained from the imbibition tests of wetting n-decane shows positive relationships with porosity and clay contents, but a negative correlation toward the TOC content. In addition, a lower-bound of the estimated permeability from wetting n-decane imbibition tests ranges from 135 nD to 528 nD, and matches well with reported measured matrix permeability.