The contribution of process and machine errors to the dimension error of machined part was investigated in this study. End milling was performed in two different types of machine configuration (XFYZ and XYFZ) in order to evaluate the dimension error caused by process and spatial errors of machine tools. The spatial machine errors were obtained by the sequential diagonal method with the Doppler laser displacement meter. For the process error, a simple average force model for a single cutting point and the identified structure stiffness is used to calculate the force induced surface error along the tool axis direction. Surface error due to tool runout effect is also considered as a contributing factor to the process error. Finally, the prediction model of dimension error for end milling was established by analyzing the machine positioning error and process error. The error prediction model was confirmed by different radial depth of cut and cutting fluid supply parameters. The dimension error of machined part was measured by the coordinate measuring machine. The experimental results reveal that the proposed model is useful in predicting the dimension error in an end milling process.