A new solid acid catalyst SO^2^-~4-MoO3-TiO2 was prepared. The activity of the catalyst in esterification of propanoic acid and n- butyl alcohol was measured and compared with that of SO^2^-~4-TiO2. SO^2^-~4-MoO3-TiO2 had better catalytic activity than SO^2^-~4-TiO2. There was evident coordination between SO^2^-~4 and MoO3 when they coexisted on TiO2.

Key words: SOLID ACID, MOLYBDENUM OXIDE, CATALYTIC ACTIVITY, SYNERGISTIC EFFECT, CATALYSIS, ESTERIFICATION, PROPIONATE, TITANIUM DIOXIDE