A speed and flux estimation method for induction motors (IMs) based on robust adaptive state observer is proposed in this paper as a modification of the adaptive state observer. The effect of gross errors on estimation accuracy of the adaptive state observer is analyzed. Whether the robust adaptive state observer can give better estimation performance and robust ability than traditional adaptive state observer for speed and flux estimation of IMs is discussed. Through the simulation and experiments, the speed estimated error and the flux fluctuation of robust adaptive state observer by gross external disturbance and internal estimated error is compared with traditional adaptive state observer. The simulation and experimental results show that the robust adaptive state observer has the better estimation performance of antigross error than traditional adaptive state observer.