The objective of this study was to explore palm oil (PMO) as a green/renewable plasticizer for ethylene propylene diene monomer (EPDM) rubber; for comparison, the commonly used plasticizer of petroleum-based paraffin oil (PO) was also investigated. The plasticization effects of PMO and PO on EPDM rubber compounds were systematically studied; in specific, the Mooney viscosity, processing properties, and cross-linking characteristics of EPDM rubber compounds with different loading amounts of plasticizer (i.e., PMO or PO) were characterized, and the mechanical properties and thermal stability of cross-linked EPDM rubber compounds were also evaluated. The results indicated that the performance/effect of PMO on processing and mechanical properties of EPDM rubber was similar/comparable to that of PO, whereas PMO is renewable with lower cost. Therefore, PMO would be a cost-effective green plasticizer that could replace PO for EPDM rubber.