Evening primrose (Oenothera biennis) is a biennial plant which its seed oil has noticeable pharmaceutical and nutritional value due to the presence of gamma linolenic acid (GLA).[1]The aim of the research was determining the effect of humic acid and biophosphore on oil content, oil yield and seed yield of evening primrose. The experiment was conducted as a randomized complete block design with three replicates. Treatments consisted of 4 level of humic acid (0, 0.1, 0.3, 0.5 %) and 2 level of biophosphore (without biophosphore or with biophosphore). The measured parameters were seed weight, oil content, seed yield per plant, oil yield per plant and oil yield per square meter. The results showed that increasing levels of humic acid were significantly decreased seed weight. Application of humic acid significantly increased seed oil content in comparison to control, but there are not significant differences between different levels of humic acid as seed oil content as concerned. Humic acid also increase seed yield and oil yield significantly. Application of biophosphore alone increased 1000 seed weight significantly, but co-application of humic acid with biophosphore decreased 1000 seed weight. In general it can be conclude that co-application of humic acid with biophosphore decreased all studied traits significantly except the seed yield.

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