In this study, an approach by the feed rate control was applied for the improvement of form accuracy in the micro end milling process. In this approach called adaptive control constraint, the feed rate is controlled so that the cutting load is constantly kept and the deflection of tool does not occur. However, this method is not always effective in the micro cutting process that the influence of size effect cannot ignore. Therefore, the relationship between the cutting conditions and the form error in the micro end milling is experimentally investigated. The experiments on the machining of metal mold steel with the micro end mill are carried out and the formulation as function of the cutting conditions and the form error is identified by means of regression analysis. The performance of the feed rate control was validated based on experimental results. As the result, it was confirmed that the form accuracy was improved.