To reduce the stitching error of circularity measurement of small cylindrical workpieces (Diameter less than 3 mm) by the segmenting-stitching method, arc contour extraction is analyzed in this paper. The coordinates of cross-sectional circle of a small cylindrical part are segmented into several equal arcs to be obtained by a two-dimensional coordinate measuring machine. The circularity contour of the small cylindrical part can be formed by stitching a series of arc contours which are calculated by the obtained arc coordinate data. Due to the different measuring pressure angles of different measuring positions, the accuracy of obtained arc coordinate points is different. The bigger the pressure angle is, the accurate the obtained arc coordinate data are. The ex-periments show that the accuracy of two ends of the arc data is not as good as the central part. Therefore, the two ends of the obtained arc data are appropriately to be cut off, namely, only the central part of the arc data are extracted to be used for the stitching. As a result, the mean value of the matching coefficient is enhanced by 12%, the deviation between the overlap part of the neighbouring arc contour is reduced by 26%, and the average curvature of the arc contours is improved with the extraction method. Thus, the accuracy of the stitched cir-cularity contour can be improved by this extraction procedure in the segmenting-stitching method for the cir-cularity measurement of the small cylindrical parts.