Cobalt substituted AlPO4-5 and AlPO4-31 molecular sieves have been synthesized hydro thermally in the presence of Co(II) species and triethyl amine and di-n-propylamine as templating molecule. Various techniques of characterization show that Co2+ cations substitute Al3+ ions in the framework. Crystals of CoAlPO4-5 and CoAlPO4-31 are relatively large, and their morphology changes with the cobalt content. Samples are thermally stable and can be calcined in air without significant loss of the crystallinity. Upon calcination, part of the Co(II) species present in as-synthesized samples are converted into Co(III) species. These Co(III) species can be readily reduced in H-2 at 400degreesC. CoAlPO4-31 has been found to be an active catalyst compared to CoAlPO4-5 in the ethyl benzene oxidation using tertiary butyl hydro peroxide.