GPR119 is a promising target for discovery of anti-type 2 diabetes mellitus agents. We described the optimisation of a novel series of pyrimido[5,4-][1,4]oxazine derivatives as GPR119 agonists. Most designed compounds exhibited good agonistic activities. Among them, compound and demonstrated the potent EC values (13 and 12 nM, respectively) and strong inherent activities. Moreover, significant hypoglycaemic effect of compound was observed by reducing the blood glucose AUC at the dose of 30 mg/kg, which is stronger than Vildagliptin (23.4% reduction vs. 17.9% reduction).