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This study was aimed at extracting and purifying T. catappa seed oil with a view to investigating the effect of processing on the composition and antioxidant activity of the oil. Oil was extracted from the dried and roasted T. catappa seed and subjected to degumming and bleaching. The different processed oils were analysed for their fatty acid, phytosterols, and fat soluble vitamins composition. Antioxidant properties of the oils were also determined by measuring the Diphenylpicrylhydrazyl (DPPH) radical scavenging activity and inhibition of heat induced peroxidation. Roasting and processing caused a reduction in acid value, increased peroxide value, but had no effect on the iodine and saponification values of T. catappa oil. Palmitic acid was the most abundant saturated fatty acid (42.466%) while oleic acid was the most abundant unsaturated fatty acid (23.445%). Roasting significantly reduced fatty acid concentration of the oil, and bleaching of both unroasted and roasted oils increased the concentration of fatty acids except linoleic acid. Gamma-sitosterol and Betasitosterol were present in appreciable amounts only in the crude oils. Roasting increased Vitamins A and D concentrations but drastically reduced that of vitamin E. Degumming had no effect on the fat soluble vitamins of T. catappa oil, but bleaching significantly reduced the concentrations of all the vitamins. The DPPH radical scavenging activity of the seed oil was between 26.93 ± 15.42% and 65.47 ± 31.59%. Refining increased the free radical scavenging activity of the unroasted oil, but did not affect the antioxidant activity of roasted oil. The capacity of the oil in preventing heat induced peroxidation was comparable to that of Butylated hydroxytoluene (BHT). Processing of the oil significantly increased its antioxidant activity. Loss of vitamin E did not affect the antioxidant activity of the oil. Thus, suggesting the presence of a heat stable antioxidant in the oil. This study indicated T. catappa seed oil to be potential pharmaceutical oil with good antioxidant characteristics