Abstract: This paper designs an observer to estimate the spacecraft’s angular velocity using only Euler angles attitude without gyroscope measurement. This work contributes as an alternative or backup system during unavailable gyroscope measurement due to faulty sensor or reduction of sensor hardware for cost reduction.In this work, the observer model for satellite attitude is derived in their nonlinear form, and the observability of the nonlinear system is investigated using Lie derivative. The performance of the designed observer is analyzed and verified using real flight data of Malaysian satellite by employing Extended Kalman Filter algorithm.