The deactivation mechanism of hollow titanium silicalite (HTS) in aqueous ammoximation of acetone was investigated. Amines and polynitro-compounds, formed by alkaline autocatalytic and oxidative coupling reaction respectively, were determined to be the main by-products. The results showed that deactivation of HTS could be caused by two main reasons: (1) slow deactivation due to by-product amines adsorbed on the active sites of catalyst surface; (2) rapid deactivation in the late period due to by-products, mainly 2,3-dimethyl-2,3-dinitrobutane (DMNB), filling and blocking the pores of catalyst. (C) 2014 Elsevier B.V. All rights reserved.