Self-pollination for five selected cucumber indeterminate inbred lines was carried out for two generations, during summer and autumn season of 2016, to confirm their purity as parents in a hybrid breeding program. Complete diallel cross among the five inbred lines were conducted during summer season of 2017 to produce all possible hybrids combinations. The twenty-five genotypes (Five parents, their 10 F₁ hybrids and 10 F₁ reciprocals) were grown and evaluated under greenhouse conditions in three sowing dates (mid of each months February, March and May respectively) for two successive years (2018 and 2019) in a randomized complete block design with three replicates. Mean performance, heterosis % and Potence ratio were estimated, for characteristics of vegetative, flowering and fruit quality, yield and its components. The results clarified that there were significant and high significant differences between genotypes of the study in all studied traits. The best parents for vegetative growth, yield components and fruit quality traits were P₄ followed by P₅ and P₂. Therefore, the three parental inbred liens P_4, P₅andP₂ can be selected as tester parents, and for the sharing in hybrid combinations to predict the best hybrids. The best hybrid combinations for most traits were found to be F₁hybrids of P₂XP₄ and P₁XP₅, and their reciprocals which recorded the highest productivity for total yield, number of fruits/plant and high average fruit weight and other fruit quality traits. Therefore, F₁hybrids P₂XP₄ and P₁XP₅ and their reciprocals could be generally, considered the most important ones and promising new produced cucumber hybrids of this study. The results proved the existence of marked potence ratios and heterosis, either over the mid-parental value or that of the better parent for all studied traits. Heterosis values for vegetative measurements, early yield, total yield, number of fruits, average fruit weight and fruit length traits were positive and significant in the most crosses, while potence ratio estimates were positive and greater than one. Therefore, the inheritance of these traits involved complete to over dominance for high over low values. However, heterosis values for flowering and fruiting measurements were negative and significant in most crosses, also potence ratio estimates were negative and greater than one. Therefore, the inheritance of these traits seemed to have dominance to overdominance nature for early over late flowering and fruiting.