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In order to investigate the effect of foliar application of humic acid on Niger (Guizotia abyssinica (L.F) Cass) under drought stress, a split-plot experiment has been conducted, based on randomized complete block design with three replications at the research farm of the faculty of agriculture/ Shahrekord University, in 2016. The main factors involve four drought stress levels (60 (the control), 100, 140, and 180 mm evaporation from the evaporation pan) and the subfactor contains four humic acid levels (0, 2, 4, and 6 L.ha-1). Results show that the influence of drought stress and humic acid have been significant on plant height, number of lateral branches, number of head per unit area, 1000 grain weight, grain yield, biological yield, harvest index, chlorophyll, carotenoids, and proline (at 1% level of probability). With the exception of proline, all of the mentioned traits are decreased by drought stress and increased by humic acid. The interaction effect of drought stress and humic acid on the number of head per unit area, crop grain yield, harvest index, proline (at 1% level of probability), and plant height (at 5% level of probability) has been significant. The maximum plant height, number of heads per unit area, grain yield, and harvest index have belonged to the control through the application of humic acid at six L.ha-1, whereas the maximum rate of proline has been observed at the treatment of 180 mm evaporation without application of humic acid. It is recommended to use 100 mm evaporation regime with application of humic acid at 4 L.ha-1 for more economic profit. The experiment shows that foliar application of humic acid under drought stress conditions could be effective in reducing stress-induced damages, during the plant growth period. [ABSTRACT FROM AUTHOR]