This study was carried out to produce promising hybrids of watermelon. Five lines i.e. Line 1 = L 84; Line 2 =  L 85 ; Line 3 =  L 94 ; Line 4 = L 84g  and  Line 5 = L 63 were used as female parents and crossed with four cultivars i.e. Tester 6 = Crimson sweet ,  Tester 7 = Charleston Gray, Tester 8 = Sugar Baby , and Tester 9 = Giza1  as male parents (testers) using a factorial mating design ,in the summer season of 2010.Twenty hybrids and their nine parents (five lines and four testers) were evaluated at the Sakha farm of Horticulture Research Institute in the summer season of 2011 along with check variety Aswan F₁ to study heterosis and combining ability. Vine length; No. of branches per plant; No of fruits per plant; average of fruit weight; total yield per plant; No. of days to maturity and total soluble solids content ( TSS) were studied. Averages of heterosis values over better parent were positively significant for many studied traits. Both general and specific combining ability were highly significant for many traits. Line 5 is a good combiner for vine length with value 15.73 and Line 1 is a good combiner for No. of branches per plant with value of 0.88. Line 2 is a good combiner for No. of fruit per plant with value of 0.46. Line 3 is a good combiner for average of fruit weight  and total yield per plant with values of 0.41 and1.43,respectively .. Line 2 and tester 8 were a good combiner for earliness with of values of -4 and -5.3, respectively, and Line 4 is a good combiner for TSS% with value of 1.19. The best crosses were, 5x6 for vine length with value of 39.67, 4x8 for No. of branches with value of 1.14, 3x7 for No. of fruit per plant with value of 1.1 and 2x8 for average of fruit weight, total fruit yield per plant  and TSS with values 1.7, 10.07and 1.13,respectively, 2x9 for earliness with value of -9.67