In order to evaluate the effect of spraying humic acid on some morphological and physiological traits of fava bean, a factorial experiment was conducted in a randomized complete block design with three replications in Chalous during 2014-16. The investigated factors included spraying time at three levels (before planting, mid-vegetative growth, and the beginning of reproductive growth) and the amount of humic acid spraying at four levels (0, 200, 300, and 400 mg/l/ha). The results of analysis of variance showed that the interaction of year × amount of humic acid on the most studied traits showed a significant difference at a probability level of 1%. Also, interaction of year × consumption time of humic acid had a positive and significant effect on dry weight of 100 seeds, grain yield, and nitrogen and potassium contents of seeds at p≤ 0. 01. Triple interaction of year × amount × consumption time of humic acid on nitrogen, phosphorus, and potassium contents were significant at p≤ 0. 05. Comparison of means showed that spraying humic acid at 200 mg /L/ha had a positive and significant effect on fresh weight of 100 seeds and grain yield. Also, spraying humic acid at 300 mg/L/ha at the second stage of vegetative growth in the second year was effective on the concentrations of potassium and phosphorus in seeds.