Despite Japanese cucumber nutritional and commercial importance, few studies have been carried out with the nitrogen (N) fertilization of the crop, especially in greenhouse conditions. This study objective was to evaluate the Japanese cucumber yield and nitrate (NO3-) accumulation in the fruits in greenhouse as a function of the N sources and doses at Viçosa, Minas Gerais State, Brazil. The experiment was set in a randomized complete block design, arranged in a 2 × 5 factorial scheme, with two N sources (ammonium sulphate and ammonium nitrate) and five N doses (0; 75; 150; 300 and 600 kg ha-1), with four replicates. The number of fruits per plant, average fruit mass, fruits yield and NO3- accumulation in the fruits were evaluated. The maximum economic efficiency N doses for two N sources used was calculated according to the prices of the fertilizers and Japanese cucumber fruits practiced in 2010. There were no significant effects of N sources and of the interaction between N sources and N doses for the productive characteristics (number of fruits per plant, average fruit mass and fruits yield) of the Japanese cucumber. However, all the productive characteristics of the Japanese cucumber increased following a quadratic model as a function of the N doses. The maximum economic efficiency N doses for the fruits yield of Japanese cucumber were 398 kg ha-1 and 386 kg ha-1, resulting in fruits yield of 76.38 t ha-1 and 76.29 t ha-1, for the ammonium sulphate and ammonium nitrate, respectively. NO3- accumulation in Japanese cucumber fruits as a function of the N doses for two N sources evaluated was not verified.