Polystyrene has long been recognized as a versatile and cost-effective material used in several industries, such as packaging, consumer electronics, building, medical, and and food service disposables. The current research focuses on the synthesis and physico-mechanical characterization of polystyrene blended with Uvaria chamae seed oil (UCSO), used as a plasticizer. UCSO was extracted with hexane and used as a plasticizer in the suspension polymerization of styrene. The findings on the quality of the oil are as follows: oil content (12.54%), specific gravity at 25 oC (0.94 ± 0.00), acid value (8.029 ± 0.12 mg KOH), iodine value (18.987 ± 0.40), peroxide value (7.0), free fatty acid (4.015%), and saponification values (173.392). The mechanical properties of the polystyrene blend with Uvaria chamae seed oil (PS-UCSO) at 100g were reported as follows: ultimate tensile strength (48.6 MPa), Young modulus (1985.3 MPa), % elongation (12.6%), break load (390.6 N), peak load (386.5 N), Shore D hardness (80.0), and water absorption (1.31%). Other properties like thermal conductivity and thermal resistance were reported as 0.2614 (W/m.K.) and 3.8256 (1/k). The findings revealed that the mechanical properties of PS-UCSO were highly competitive with the conventional white petroleum oil used as a plasticizer. As a recommendation, Uvaria chamae seed oil should be used as a plasticizer since it is available, cheap, and environmentally friendly.