This paper presents a methodology to calibrate kinematic parameters in a Hexapod-type parallel mechanism machine tool. In the conventional calibration process, the influence of the calibration error and that of the deformation of struts due to the gravity cannot be explicitly distinguished on contouring error trajectories. As a result, the gravity-induced contouring error becomes one of major causes for calibration error of kinematic parameters. This paper presents a kinematic calibration methodology that takes gravity-induced errors into explicit consideration. By performing the calibration of kinematic parameters and the modification of the prediction model of gravity-induced errors in an iterative manner, the machine's contouring accuracy can be improved. Experimental comparison shows the machine's contouring accuracy is significantly improved by applying the proposed calibration method.