Abstract: The effects of exogenous hormones KT and IAA in the derooted seedlings of Cucumis sativus L. on polyamines in vitro and the formation of female flowers were studied in this paper. It was found that the induction rate of female flower in derooted seedlings cultured on MS mixed with 3.0 mg/L KT and O. 01 mg/L IAA accounted for 28%, whereas the control was 0. It was observed that during the formation of female flower, the content of endogenous Spd and the ratio of Spd to Put in derooted seedlings apparently exceeded those in the control. It revealed that high levels of Spd and the ratio of Spd to Put in derooted seedlings could promote the formation of female flowers. No significant difference existed in the endogenous Spin between treatment of 3.0 mg/L KT+0. 01 mg/L IAA and control, except for the induction rate of female flowers. It indicated that Spin had no direct effects on the formation of female flowers. The levels of DAP in derooted seedlings cultured on MS mixed with 3.0 mg/L KT and 0.01 mg/L IAA were apparently lower than that in control. It was seen that exogenous hormones could promote the formation of female flowers in derooted seedlings by reducing the catabolism of polyamine. However, the levels of Cad in derooted seedlings cultured under the same condition mentioned above were higher than that in control and its emergence was prior to control. It showed that Cad was a kind of material produced from physiological metabolism during formation of female flowers instead of the effect factors.