Abstract: Effects of H2O on catalytic reaction system for reductive alkylation of p-aminodiphenylamine/MIBK was studied. Platinum nanoparticles supported on activated carbon with high specific surface area was used as a catalyst for reductive alkylation reaction under different H2O content conditions. Schiff base forming datas, catalytic activity and stability of the catalyst were investigated under aforementioned reaction conditions. Fresh and used catalysts were characterized by SEM, TEM, ICP, XRD,BET and particle size analysis. The results indicated that H2O could decrease schiff base formation rate, catalytic activity and stability, making the structural damage of the supports and the grain aggregation, exacerbating Pt loss and enrichment of contaminating metal elements,while dewatering was significative on this problem.