Cucurbita is one of the most economically important vegetable crops. Summer squash is the most widely grown amang Cucurbita. Some of the plant growth regulators (PGR) have important effect on sex expression in various cucurbitaceae plant. Also, by decreasing or increasing the male or female flowers, it causes change in yield. To study the effect of spermidine and methyl jasmonate on sex expression on Cucurbita pepo L. cv. ideal .Two experiments were conducted in Isfahan University of Technology, Isfahan Iran, in a completely randomized block design with three replication in during the spring, summer and autumn of 2015. The first experiment was conducted during the spring until middle summer. Treatment consisted of spermidine at a concentrations of 0.03 and 0.07 and methyl jasmonate at concentrations of 0.5 and 0.75 mM and distilled water as control Treatment. Plants werefoilar sprayed at the 4-2 leaf stagethe. the factor of time of flowering, the number of female and male flowers, the ratio of female to male flowers, flowering index, yield (fruit number and weight of fruit), the weight of a fruit, levels of carotenoids and chlorophyll leaf and fruit, fruit firmness, total soluble solids of fruit, vitamin C content of fruit, the antioxidant activity of fruit, fruit color quality index, main stem length plants, crown diameter, number of nodes and dry weight were evaluated. In order to evaluate more accurate the effect of growth regulators on on sex expression of summer squash, Another experiment by changing concentrations, was conducted in the end of summer to middle fall. Treatment consisted of spermidine at a concentrations of 0.1 and 0.5 and methyl jasmonate at concentrations of 0.5 and 0.75 mM and distilled water as control Treatment. factor of first flowering node, the number of female and male flowers, the ratio of female to male flowers, yield (fruit number and weight of fruit), the weight of a fruit, levels of carotenoids and chlorophyll-leaf and fruit, vitamin C content of fruit and the antioxidant activity of fruit were evaluated. The results of the first experiment showed that: Spermidine increased the number of female flowers, but had no significant effect on other reproductive traits. Methyl jasmonate, number of female and fruit weight increased compared to control. Spermidine and methyl jasmonate increase in fruit firmness compared to controls and spermidine 0.07 mM showed the greatest increase in fruit firmness, in the event that The treatments had no significant effect on the total soluble solids of fruit, vitamin C content of fruit, the antioxidant activity of fruit, fruit color quality index. Spermidine showed no significant difference in the amount of chlorophyll in the leaves and fruit and fruit carotenoid. methyl jasmonate 0.75 mM increased amount of carotenoids in leaves compared to other treatments, in the event that there was no significant difference in the amount of other chlorophylls. Spermidine 0.07 mM and methyl jasmonate 0.75 and 1 mM were increased during the main stem length but had no significant effect on the number of nodes, crown diameter and plant dry weight. The results of the second experiment showed: Spermidine had no significant effect on first flowering node, the number of male and female flowers, the ratio of male and female flowers and yield. Spermidine had no significant effect on plant reproductive traits. methyl jasmonate 1 mM ratio of female to male flowers increased but had no significant effect on other reproductive traits. Spermidine vitamin C content of fruit increased compared to control, in the event that methyl jasmonate did not show significant differences. Spermidine 0.5 mM increased total chlorophyll and chlorophyll b fruits were compared with control and methyl jasmonate, in the event on the other chlorophyll did not show significant differences. Methyl jasmonate leaf carotenoid content increased compared to control. and methyl jasmonate 0.75 mM reduced total chlorophyll fruits and on the other chlorophyll showed no significant difference. The results of both experiment showed: The treatments had no significant impact on sex expression and reproductive traits and had the most influence on the physico-chemical characteristics that can affect the nutritional value of plants. Key words : Spermidine, methyl jasmonate, sex expression, summer squash