To better understand the characteristics of nanopores and their influence on methane adsorption capacity of shales, we have conducted fractal analysis for 6 fresh shale samples from the Sichuan Basin in southwestern China. Isotherms of nitrogen gas adsorption/desorption analyses indicate that shales have distinct adsorption characteristics at relative pressure of 0-0.5 and 0.5-1. Two fractal dimensions D1 and D2 were obtained using the fractal Frenkel-Halsey-Hill (FHH) method. The two fractal dimensions, D1 and D2, have different correlations with methane adsorption capacity of shales. Methane adsorption capacity increases as D1 and D2 increase, and D1 has greater impact on the adsorption. Further investigation indicates that D1 represents fractals from pore surface area generated by surface irregularity of shales, while D2 characterizes fractals related to pore structures that are controlled by the composition (e.g., TOC, clay minerals, quartz) and pore parameter (e.g., pore diameter, micropores content) of shales. Higher fractal dimension D1 corresponds to more irregular surfaces that provide more space for methane adsorption. Higher fractal dimension D2 represents higher heterogeneity of pore structure and higher capillary condensation on pore surfaces that increase methane adsorption capacity. Therefore, more irregular shale surface and more homogeneous pore structure result in higher methane adsorption capacity of shales.