A resin formulation is provided. The resin formulation includes carboxy anhydride at 100 parts by weight, first diisocyanate having the following formula (I) at 20-90 parts by weight, second diisocyanate having the following formulas (II), (III) or a combination thereof at 45-103 parts by weight, and bismaleimide (BMI) at 50-200 parts by weight. A resin polymer and a composite material including the resin polymer are also provided. In formulas (I), (II) and (III), A includes benzene or cyclohexane, Q includes C1-C12 alkylene, —O—, —S— or —SO2—, X includes —H, —CH3 or —CH2CH3, R1 includes —H, —CH3 or —CH2CH3, and E includes —H, —CH3 or —CH2CH3.