In this work, a simple but effective approach was reported for preparing natural fiber reinforced plastic foams based on plant oil with excellent compressive performance and biodegradability. Firstly, epoxidized soybean oil (ESO) was converted into its acrylate ester AESO, which can be free-radically copolymerized with reactive diluents like styrene to give thermosetting resins and their foam plastics. Then the bio-foam composites were produced using short sisal fiber as the reinforcement. Effects of fiber loading, length and surface treatment on properties of the foam composites were investigated. It was found that exposure of the fibers to gas cells of the foam reduced the effectiveness of interfacial effect, which is different from conventional bulk composites. As a result, reinforcing ability of sisal fibers became a function of fiber length, loading, etc. Furthermore, the plastic foams based on plant oil resin were proved to be biodegradable in soil burial or in the presence of fungi.