Abstract: Effects of negative oxygen ions on the growth and development of cucumber (Cucunis sativus L. ) were studied. The results indicated that negative oxygen ions promoted the growth of vegetative organs at seedling stage, inhibited growth at the blossoming stage, lowered the node position of the first female flower, increased the percentage of fertile plant and yield of single plant and pro longed the time of fruiting. The output had been increased by 13. 1 % in comparison with control. On the basis of analyses of expcrimen tal results, it is suggested that the effect of negative oxygen ions on the growth and development of cucumber was related to promotion the synthesis of endogenous phytohormones and enhancement the activity of some enzymes.