Mesoporous Mn-MCM-41 (Si/Mn = 29, 56, 73 and 104) materials were synthesized by hydrothermal process. Their structures were characterized by X-ray diffraction (XRD). Surface area, pore size and wall thickness were calculated from BET equation and BJH method using nitrogen sorption technique. The thermal property of the as-synthesized materials was studied using thermogravimetric-differential thermal analysis (TG-DTA). Diffuse reflectance UV-Vis spectroscopy confirmed presence of manganese ion in the framework position of the MCM-41. Mn(II) species with a well-resolved singlet, centered at g = 2.007, was assigned to have distorted tetrahedral symmetry. The oxidation of ethylbenzene has been carried out over Mn-MCM-41 (Si/Mn = 29, 56, 73 and 104) using t-butylhydroperoxide as oxidant at 333-353 K. Mn-MCM-41 (29) was more active than other catalyst, and it retained activity for three cycles of operation. The major products were alpha-phenylethanol and acetophenone. Benzaldehyde and phenyl acetaldehyde were also observed in minor quantity. The difference in the product selectivity was explained based on the reaction intermediates. (C) 2004 Elsevier B.V. All rights reserved.