Disclosed is a modified polyisobutylene polymer for rubber compounding. The modified polyisobutylene polymer is prepared by reacting reactants including a polyisobutylene in which the main chain is isobutylene, an unsaturated dicarboxylic anhydride, and an amino group-containing silane compound. The modified polyisobutylene polymer includes a diamide structure. When the modified polyisobutylene polymer is used as an additive for rubber compounding, the processability of the rubber is increased, the dispersibility of fillers is significantly improved, and the effect of obtaining excellent grip performance and improved rolling resistance can be achieved.