Abstarct: Population growth and overuse of water resources have resulted in reduction of agricultural water resources. Therefore it is necessary to achieve appropriate methods to increase productivity in the agricultural sector. The application of organic inputs like Humic acid, which have hormone-like activity, can increase the adsorption of water and minerals by the plant with minimum damage to environment. An experimental research as randomized complete block design with three replications was conducted to study the interaction of factorial arrangement of Humic acid and drought stress on growth and yield of potato in research Farm of Shahrood University of Technology. The factors were 4 foliar application levels of Humic acid {zero (control), 800, 1600 and 2400 ml/ha} and 3 levels of irrigation {7-day surface irrigation (control), 14 days and 21 days respectively}. The results showed that the simple effects of factors were significant on traits. The 2400 ml/ha foliar application of Humic acid increased traits like tuber diameter, tuber dry weight and tuber yield. Irrigation at any level decreased tuber yield compared to control. The interactive effect of Humic acid and irrigation on tuber yield appeared to be significant. The concentration of Humic acid used at each level of irrigation increased leaf area index and plant biomass. The results of this research clearly indicated that the application all levels of Humic acid could alleviate the deleterious effects of drought stress.