Oil extracts of sweet orange (Citrus sinensis) seeds and peel were examined for their effects on Gmelina arborea wood as preservative chemicals. Wood samples of Gmelina arborea were Oven dried and treated with oil extracts from the seeds and peels of Citrus sinensis at 0%, 25%, 50%, 75%, 100% concentration levels and exposed to fungi attack for a period of 12 weeks. The percentage weight loss of the wood samples after fungi attack was assessed and data were processed by Analysis of variance. The absorption of preservative varied in respect to concentration levels in the wood samples which ranged with a mean value of between 13.98±3.17 and 15.83±2.20. The percentage weight loss was significantly high with the samples without treatment (the control) compare to wood treated with preservative level. The concentration level of preservative was significant at (p≤0.05). The highest concentration (100%) had the lowest mean values of weight loss of 11.75±4.44 and 8.19±1.44 with both seed and peel oil extracts respectively. The level of effectiveness exhibited by the bio preservative Citrus sinensis oil extract thus shows the need to exploit the development of other forms of natural based plant preservatives for protection of wood and wood products in service.