Irvingia gabonensis (Aubry-Lecomte ex O'Rorke) Baill seeds are often contaminated in storage by postharvest spoilage fungi. This study investigated the nutritional contents of the seeds, phytochemical contents and antioxidant activity of different parts of the plant as well as their antifungal effects against fungi isolated from the deteriorated seeds. Proximate, mineral and phytochemical analyses were carried out using standard laboratory techniques. The antioxidant activity was against DPPH radicals. Ethanol extracts (100 and 200 mg/ml) of the various parts were screened against the isolates using pour plate method in Potato Dextrose Agar (PDA) plates. The plates were examined for growth daily for 10 days. Data were statistically analysed. The healthy seeds contained higher protein (13.73%), fat (58.73%) and fibre (2.50%), whereas, higher content of moisture (10.17%) and carbohydrate (15.47%) were observed in the spoilt seeds. The leaf had highest contents of alkaloids (1228.3 mg/100 g), flavonoids (1345.9 mg/100 g), tannins (1345.9 mg/100 g), saponins (578.3 mg/100 g) and carotenoids (2348.3 μg/100 g). The antioxidant activity of the leaf (50.30%) was the highest. Fungi isolated from the deteriorated seeds were Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus and Curvilaria lunata. The leaf was most effective against A. niger, A. flavus and C. lunata whereas the stem bark extract was most effective against A. fumigatus. The F-values were significant for model, treatment, concentration and number of days for the leaf and root. This study confirmed the antifungal activity of extracts of various parts of the plant against isolates implicated in the deterioration of its seeds. The extracts could be used as preservative to enhance the shelf-life and nutritional quality of the seeds. Keywords: Irvingia gabonensis, Spoilage of seeds, Antifungal activity, Free radical scavengers, Preservatives