Hydroponic growth systems are expanding due to their advantages such as maximum yield, healthy crop production and reduced labour requirement. Vegetable in each stage of the plant growth needs adequate nutrients in different growing media. The objective of this study was to examine the effect of some growth media on N, K and Mg uptake by greenhouse cucumber. This study was carried out in the research greenhouse of Islamic Azad University-Khorasgan branch, using a completely randomized design with 5 treatments, 4 replications and 10 plants in each replication. The Five different growth media consited of pure cocopeat, perlite-cocopeat (50-50 v/v), perlite-cocopeat-peatmoss (50-20-30 v/v and 50-30-20) and perlite-peatmoss. Physical and chemical properties and some nutrients concentrations such as N, K and Mg as well as fruit yield were examined. Although no significant difference was found among the studied growth media in the fruit yield of cucumber, the highest yield was obtained for cocopeat. Significant difference (P<0.05) was observed in the plant biomass among the growth media. The highest biomass was obtained for the cocopeat and perlite-cocopeat media. No significant difference was found among the growth media in concentrations of N, K and Mg although the highest concentrations of N and K in the second and third stages of sampling were obtained in cocopeat. Shoot concentration of Mg at the first and second stages of sampling was more than the critical deficiency level. The best concentration of Mg was obtained in cocopeat. In general, the best nutrient concentration and yield were found in cocopeat substrate which can be used as an appropriate growing cucumber media for in soilless culture.