V- MCM- 41 mesoporous molecular sieves with similar vanadium content (similar to 0.6 wt.%) and surface area (similar to 700 m(2)/g) but different pore sizes ( from 1.8 to 2.9 nm) were synthesized. A pore wall radius of curvature effect on the initial rate of catalytic reaction existed when the cyclohexene epoxidation was used as a probe reaction, the larger the pore size, the higher the initial reaction rate. However, the turnover frequencies over a long period ( 72 h) were constant respect to different pore diameters, which was probably due to the strong pore diffusion limitation in the liquid environment.