The synthesis of allantoin from carbamide and ethyl aldehydic acid with rareearth solid superacid SO2-4/TiO2La3+as catalyst was studied.It was found that the optimal experimental conditions were that La3+/TiO2 was immersed for 12h and backed at 550℃ for 3h;the yield of the allantoin could reach up to 745% under molar ratio of carbamide and ethyl aldehydic acid 35∶1,amount of SO2-4/TiO2La3+ solid superacid catalyst of 10g(if the weight of ethyl aldehydic acid was 01mol),the reaction temperature of 73℃～75℃ and reactiom time of 3h. The synthesis of allantoin from carbamide and ethyl aldehydic acid with rareearth solid superacid SO2-4 / TiO2La3 + as catalyst was studied.It was found that the optimal experimental conditions were that La3 +  / TiO2 was immersed for 12h and backed at 550 ℃ for 3h; the yield of the allantoin could reached up to 745% under molar ratio of carbamide and ethyl aldehydic acid 35:1, amount of SO2-4 / TiO2La3 +  solid superacid catalyst of 10g (if the weight of ethyl aldehydic acid was 01mol), the reaction temperature of 73 ℃ ~ 75 ℃ and reactiom time of 3h.