This paper presents an accurate optical technique for sphericity measurement of a ball by means of phase shift interferometry. The ball is placed in a fixture on a numerically control rotary stage to achieve a 360 degrees inspection. A CCD camera is used to capture the images of interference fringes, and the generated interferograms are used to calculate the phase values which can then be used to quantify the sphericity error. With the calculated phase values, the eccentricity of the rotary stage's spindle can be estimated and compensated. The Zernike polynomials is employed in the process of calibration to gracefully remove defocus and tilts. The experimental procedure, the sphericity measurement results and their statistical data analysis are presented.