Combining ability and heterosis were studied in a 6×6 partial diallel cross during 2007-2009 to see the nature of gene action in cucumber (Cucumis sativus L.). Analysis of variance revealed high significant differences among all the F1 hybrid means and among their respective six parental values for all the traits examined. The mean squares attributed to General Combining Ability (GCA) and Specific Combining Ability (SCA) were also highly significant. SCA genetic variances were greater than those of GCA and more important for the traits of Marketable Yield as well as Simple Weight Index, showing the dominance of non-additive gene action. Early yield and nonmarketable yield were controlled by additive and non-additive type of gene action due to high GCA variances. Line 504 with its bearing of high general and specific combining ability is finally found desirable regarding cucumber hybrid seed production and therefore is recommended.