In this study an integrated Algebraic method/Extended Kalman fitler (EKF) attitude determination system is presented, in which the 2-vector and EKF algorithms are combined to estimate the attitude angles and angular velocities. As a reference directions for algebraic method, the unit vectors toward the Sun and Earth's Magnetic Field are used. The Euler angles produced 2-vector algorithm and their error variances are provided as input to the EKF. Then the EKF uses this attitude information as the measurements for providing more accurate attitude estimates even when the satellite is in eclipse. The "attitude angle error covariance matrix" calculated for the estimations of the algebraic method are regarded as the measurement noise covariance for the EKF. The parameters of satellite's rotational motion (Euler angles and angular velocities) are estimated using EKF. In comparison to more traditional approaches, this preprocessing step significantly reduces the complexity of filter design by allowing the use of linear measurement equations.