The crater size-frequency distribution curve for the lunar surface has a bending point near 4 km in diameter. It is suggested that the steepening in the smaller diameter range is caused by the effects of secondary craters and/or size-frequency distribution of the impactors. In order to extract the fraction of the primary craters created by Near Earth Objects, among the primary-secondary mixture of km-size craters, we have examined the crater shape statistics using Clementine images of the lunar surface. We found that the size-frequency distribution of the craters with ellipticity smaller than 1.2 can be considered primary craters generated by impactors from interplanetary space. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.