Combining ability and heterosis effect of mine inbred lines of <Cucurbita maxima Duch.> was estimated. As a result of incomplete diallel crosses 49 hybrids were obtained and then they were evaluated in two years of experiment. Both GCA and SCA were estimated. Heterosis effect was tested by comparison to the better parental form. <Hybrids value> was also estimated by comparison to the standard and by Pollhamer method. High GCA values were indicated for such traits as fruit weight and number, <fruit yield> <dry matter content> and yield. Significant SCA was observed for fruit yield. It confirms the contribution of the other than additive gene action. With respect to dry matter content and yield 144 line appeared to be the best parental form. Reciprocal crosses had an important effect on fruit vield and fruit weight. The highest heterosis effect was observed for dry matter yield and dry matter content.