Phenolic compounds in macadamia nuts and shells were identified, and their antioxidant activities were evaluated in refined macadamia nut oil. Thin-layer chromatography of oil extracted from macadamia nut kernels and shells indicated the possible presence of catechol, phrogallol, and 3,4,5-trihydroxy phenolic compounds. Four phenolic compounds were tentatively identified as 2,6-dihydroxybenzoic acid, 2′-hydroxy-4′-methoxyacetophenone, 3′,5′-dimethoxy-4′-hydroxyacetophenone, and 3,5-dimethoxy-4-hydroxycinnamic acid. Adding 0.01% of 2′-hydroxy-4′-methoxyacetophenone, 3′,5′-dimethoxy-4′-hydroxyacetophenone, or 3,5-dimethoxy-4-hydroxycinnamic acid to the oil significantly increased the Rancimat induction time against the control (P<0.0001). At this concentration, 3′,5′-dimethoxy-4′-hydroxyacetophenone was the most effective compound added. Although induction times of oils with 0.01%, 2,6-dihydroxybenzoic acid were not significantly different from the control, at 0.1% there was a significant difference from the control (P<0.0001). The activity was the same as that of 2′-hydroxy-4′-methoxyacetophenone at 0.1%.