This study was aimed at evaluating the effect of oil extraction in spent coffee ground (SCG) on the properties of spent coffee ground-polypropylene composites. Coffee oil was removed from SCG by ultrasonication extraction. SCG and extracted spent coffee ground (ESCG) were used to reinforce the polypropylene (PP) in this research. Moisture uptakes, morphologies, mechanical properties, thermal properties, and accelerated aging test of composites were examined as a function of oil extraction. The results suggested that the extraction of coffee oil improved the water resistance of composites. The mechanical properties of spent coffee grounds-polypropylene composites (SCGPCs) were improved significantly after oil extraction, which suggested that the oil extraction was helpful to improve the interfacial adhesion and compatibility between filler and PP matrix. The moisture absorption of SCGPC showed a dramatic decrement after oil extraction. The results also revealed that the oil extraction improved the thermal property of composite.