This paper considers the rotor speed and flux estimation for induction motors, which is one of the key problems in speed-sensorless motor drives. Existing approaches, e.g. adaptive, Kalman filter-based, and sliding mode observer, have limitations such as unnecessarily assuming the rotor speed as a constant parameter, failure to ensure convergence of estimation error dynamics, or conservative design. This paper proposes a nontriangular observable form-based estimation algorithm. This paper presents realizable observers to avoid transforming the induction motor model into the form. Advantages of the new estimation algorithm include guaranteed stability of estimation error dynamics, constructive observer design, ease of tuning, and improved speed estimation performance. Finally, experiments are conducted to demonstrate the effectiveness of the proposed estimation algorithm.