The use of anhydrous urea-hydrogen peroxide adduct as an oxidizing agent in the epoxidation of styrene catalyzed by a titanium-silicate (TS-1) molecular sieve resulted in very high selectivity (similar to 85%) for styrene oxide. When aqueous hydrogen peroxide (H2O2) was used for styrene epoxidation, the styrene oxide selectivity was very poor (5-10%) mainly due to its isomerization into phenylacetaldehyde. The formation of different types of Ti-superoxo complexes was also observed by the solid-solid interaction with anhydrous urea-hydrogen peroxide and TS-1. It was confirmed by the characteristic continuous absorption band in the UV-Vis region (300-500 nm) and also by an intense and anisotropic EPR spectrum for the superoxide radical ion stabilized on Ti (IV) centers of TS-1 samples.