This study was achieved during the first of March 2021, 2022 and 2023 seasons in Kaha Farm, Horticultural Research Institute, Agriculture Research Center at the Qalyobiya Governorate, Egypt. The purpose of this investigate was to estimate hybrid vigor and combining ability of some watermelon hybrids. A total five watermelon inbred lines (genotypes) crossed in a half diallel mating design to obtain 10 cross combinations (F1 hybrid). All genotypes were prepared at Randomized Complete Block Design with thrice replication. The data showed that significantly differences between the crosses and their parents for traits. The data exhibited that some F₁hybrids recorded highly significant to mid and better parent's heterosis for traits. The best crosses for most studied characters were P₁ x P₂, P₁ x P₄ and P₄ x P₅, Thus these promising crosses to improve the yield and quality in watermelon. GCA and SCA influences were significant for plant traits. GCA/SCA ratio were lower than unity for plant length and TSS traits, indicating that dominance types of gene effect were higher importance in the inheritance of traits and seems to be predominant with a possibility of exploiting heterosis to boost the yield. The evaluation of combining abilities revealed that the parents P₁, P₂ and P₄ were identified as the ideal general combiners for generality traits and the F₁ hybrids P₁XP₂ and P₁XP₄ were the better specific combinations for total yield and associated traits. Therefore, these F₁ hybrids are promising crosses with high yield and quality which can be recommended for commercial cultivation.