Liquid-phase epoxidation of alkenes and hydroxylation of phenol were carried out using TS-1 titanosilicate as a catalyst with the particle sizes ranging from 0.15 up to 25 A mu m. Experimental reaction rates as measured on the smallest catalyst particles were found to be free of mass transfer influence. This makes it possible to describe quantitatively the internal diffusion effects for large-size grains, so as to evaluate the values of reagent diffusion coefficients within the catalyst pores [GRAPHICS] .