Laser Raman spectroscopy has been used to study the interaction of $MoO_3$ with $TiO_2$. The bulk molybdenum oxide appeared to spread on the surface of titania under the submonolayer coverage. The surface polymolybdate was observed to be very stable with respect to the repeated treatment of reduction and subsequent calcination. Owing to the interaction of molybdate and titania, the phase transformation of $TiO_2$ seemed to be strongly retarded. The additives such as Co and Ni reacted readily with $MoO_3$ to form the corresponding molybdate salts. Nevertheless, the polymolybdate species appeared to be more stable on the titania surface than the molybdate salts.