Abstract: Considering the requirement of micro cutting tool, a new kind of micro ball-end mill was proposed based on the elliptic ball-end mill which was introduced by Aoyama, Kishinami and Saito. A mathematical model of this new tool was established by using differential geometry to obtain the angles of cutting tool in tool-in-hand system. Through the analysis of the manufacturing process of the tool, an optimal structure of the tool was designed eventually. This new designed tool could meet the need of cutting condition. It also has a stronger cutting edge and is easier to be manufactured.