Pore structural framework of Lower Permian shales from two Indian basins is investigated using a low-pressure nitrogen adsorption-desorption technique. Specific surface areas (SSA) of shales are controlled by their thermal maturity. Thermally mature shales are marked by lower average pore sizes, diminishing pore size distribution style from the finer to the coarser pores, and higher fractal dimension D2, relative to the less mature shales. D2 (pore structural fractal dimension) showed a positive relationship with SSA and maturity and a negative correlation with pore sizes. The fractal-distinguishing parameter increment S was higher for the mature shales. With increasing maturities, pore structures become complex and the fractal dimensions become more distinct.