The classificaiton_extendedness parameter, which is based on the difference between the CModel and PSF magnitudes, is stored in the database and is a reasonable star/galaxy classifier.  Using the star/galaxy separation from HST/ACS in COSMOS as the truth table, here we characterize the accuracy of our star/galaxy separation.  The completeness is defined as a fraction of ACS stars properly classified as stars in HSC. The contamination is a fraction of ACS galaxies among objects classified as stars in HSC.  Both the completeness and contamination rates are strong function of the seeing size and depth.