Abstract: The optimum nitrogen application rates for best economic benefits in five vegetablecrops were investigated under greenhouses which have been cultivated for six to ten years in Zhangye.The results showed that the nitrogen application rates were positively correlated to the yields of zucchini, cucumber, eggplant, pepper and tomato, and the correlation coefficient were 0.8388, 0.8812, 0.8044, 0.8418 and 0.9058,respectively.Though the yields were increased with the increase of nitorgen application rates, the profit margins and yield increase by unit nitrogen applied decreased, i.e.showing the diminishing return.The regression analysis indicated that the optimum nitorgen rates for best economic benefits in zucchini, cucumber, eggplant, pepper and tomato were 450 kg·hm^-2,360 kg·hm^-2,240 kg·hm^-2,420 kg·hm^-2,480 kg·hm^-2 respectively;and the theoretical yield was 129.7 t·hm^-2,96.2 t·hm^-2,82.5 t·hm^-2,69.3 t·hm^-2 and 105.7 t·hm^-2;respectively;which was consistent with the results of field experiments.