The liquid-phase ammoximation of various ketones to the corresponding oximes with ammonia and hydrogen peroxide was conducted over titanium mordenite (Ti-M) prepared from dealuminated mordenites and TiCl4 vapor by a secondary synthesis method. The catalytically active sites, the effects of reaction variables and residual Al within Ti-M on the ammoximation performance and the shape-selectivity for various ketones were studied to clarify the reaction mechanism for the liquid-phase ammoximation. The ammoximation was catalyzed effectively by tetrahedrally coordinated Ti atoms in the framework sites in the presence of water at an optimum reaction temperature of 333 K. There was no direct correlation between the ammoximation activity and the molecular size of ketone. Ti-M was even active for bulky ketones which were hardly adsorbed into the pores. The ammoximation has been proposed to proceed through a consecutive reaction, including the oxidation of NH3 by H2O2 over Ti sites to form a hydroxylamine intermediate, and the subsequent reaction of hydroxylamine with ketone mainly in the solution to give oxime. The second-step reaction has been suggested to be the rate determining step in the ammoximation.