The use of organic materials to increase the quantity and quality of the agricultural products and prevent the over-application of chemical fertilizers is one of the new solutions in sustainable agriculture. Humic substances are considered as one of the most important organic sources that have a behavior similar to growth stimulants, especially auxin hormones, and can also increase the absorption of nutrients by the plant. In this study, the effect of humic substances on growth and nutrient content of maize plant under controlled greenhouse conditions was investigated. In the first step, humic substances were extracted from the Leonardite powder using a 0.1 M KOH solution. The extracted humic substances were used in a greenhouse experiment, after identification of its functional groups and elemental composition. For this purpose, maize seeds were sown in pots containing quartz sand media. The experimental treatments consisted of a concentration factor of humic substances in six levels (0, 20, 40, 80, 200 and 400 mg/L). The pots were kept under greenhouse conditions for 50 days and were irrigated with tapwater to 60% water holding capacity of the medium. In addition, the plants were treated once a week with a Johnson nutrient solution and the solution containing humic substances. At the end of the experiment, root and shoot dry weights and the absorption of macronutrients and micronutrients by the plants were measured. The results showed that the use of humic substances increased the dry weight of root and shoot of maize, which was more pronounced in root. Also, the use of humic materials led to an increase in total phosphorus, potassium, calcium, magnesium and copper Contents in root and shoot shoots of maize. Generally, the most effective concentration of humic substances in relation to nutrient uptake efficiency and root and shoot dry weight production was 400 mg/L. It can be concluded that humic substances can be desirably used as good organic conditioners for increasing the production of crops and improving the efficiency of chemical fertilizers. Keywords: Organic matter, Humic acid, Plant nutrition, Hydroponics