Abstract: A kinematics parameter calibration method for serial robots based on the product of exponential (POE) formula is presented. According to the adjoint transformation between the theoretical value and actual value of joint twists, the POE formula is transformed into an equivalent form including the joint constraints. A linearized model describing the relationship between the errors in the end-effector and the errors in the joint twists and in the zero position twist, is obtained by differentiating the kinematics equation. A least-squares kinematics calibration model for serial robots is given and the joint twists are updated through the adjoint transformation in the kinematic parameters identification procedure. A calibration simulation experiment with a 6-DOF (degree of freedom) serial robot shows that the calibration process can quickly converge to the stable values and the calibration result can compensate for the pose errors in the end-effector effectively.