Using adequate nitrogen (N) supply is one of the main goals of sustainable plant production. Excessive application leads to health, environmental and economic problems. Horticultural systems are more sensitive but beside the question of sustainable agriculture, the demand for N fertilizers remains strong. Being 'green', but satisfied, we need to know the exact amount of N, which is sufficient and no more, or need to find efficient genotypes for adequate N use efficiency. The objectives of this research were to investigate photosynthetic capacity of cucumber (Cucumis sativus L cv. Rajnai fürtös) seedlings under different amount of N supply (5 times, half times, tenth of optimal N in the nutrient solution) in hydroponic conditions. The dry weight of root and shoot, the relative chlorophyll content (SPAD value), photosynthetic pigments content and optimal photochemical activity (Fv/Fm) were measured. The half reduction of optimal N supply did not reduce our measured parameters, the relatively large nitrogen deprivation did not cause significant differences compared to the optimal nitrogen supply.