In recent years, the intensive usage of either pesticides or overdose of fertilizers caused both an increase in plant production and showing up some products which would threaten human health. The chemicals (pesticides, fertilizers, etc.) which are being used in agricultural production, have made their potential negative influence both on human and society health evident. For that purpose, as a new mode of production "Organic Farming" manifested itself. In organic fresh vegetable growing, one of the most important topics which still needs to be studied is "plant nutrition". The most important deficiency in plant nutrition is "nitrogen nutrition". Nitrogen is the most commonly used plant nutrient element in production. Nitrogen sources that are being used in organic production are limited and their pure nitrogen contents are weak. Cucumber, is the second most grown vegetable just after tomato in greenhouses in Turkey. It is consumed both winter and summer and it is also a vegetable which is on the market the whole year. Besides, because of its long vegetation time and its tendency of making much vegetative texture, it is one of the most nitrogen using vegetables. This study was carried out in the greenhouses of Cukurova University, Karaisali Vocational College in Adana, in order to determine the optimum nitrogen dosage to be applied in organic cucumber production under greenhouse circumstances of the spring season. For this purpose, a common organic certified fertilizer was applied as the nitrogen source contending 10.21% pure nitrogen was used. The nitrogen doses of 0, 0.5, 1.5, 2.5 and 3.5 kg ha(-1) were applied, in total six applications. During the trial, in order to investigate the effects of different nitrogen dosages on plants growth parameters were measured. Also, nutrient element contents of leaves were analyzed, fruit physical characteristics and the yield values were measured. Consequently, it was determined that top two nitrogen dosages (2.5 and 3.5 kg ha(-1)) increased the plant growth. In terms of the yield, it is concluded that the dose of 1.5 kg ha(-1) would be enough for increasing this parameter.