CdS nanoparticles, prepared in reverse micellar systems, were incorporated into thiol-modified MCM-41 (FM41) mesoporous material, of differing pore sizes, designated as large (L-FM41), middle (M-FM41), and small (S-FM41). A particle-sieving effect of the FM41 was observed, in that the incorporation of the CdS nanoparticles was decreased by increased size of particle, and by a decreasing pore size of the FM41. The resulting CdS-FM41 composite showed photocatalytic activity for H-2 generation from water.