This work was carried out at a private farm at Kafr Abou EL Hadeed, Giza Governorate, in the summer and fall plantings of summer squash (Cucurbita pepo L.) during 2002-2003, 2003-2004, and 2004-2005 seasons. Four Egyptian and Syrian summer squash cultivars (Eskandarani, Balady, Gabla, and Halap) were used. Four generations of inbreeding and selection were carried out and 8 strains of summer squash were obtained, namely E1, E2, B1, B2, G1, G2, H1, and H2. The selected lines recorded significant increment in most studied characters comparatively with their original populations, especially in number of pistillate flowers, fruit weight and early and total yield. On the other hand, most of selected lines recorded significant decrement in number of staminate flowers and sex ratio. These selected lines can be used later in a breeding program to produce new summer squash hybrids.