Poly(3-hydroxy alkanoate) containing unsaturated side chains was produced by feeding Pseudomonas oleovorans with soybean-oil acid (PHA-soybean). The composition of PHA-soybean were found to be 10 mol-% of unsaturated side chains with the saturated hexanoate, octanoate and decanoate units. Methyl methacrylate (MMA) was thermally grafted on PHA-soybean in the presence of benzoyl peroxide, Fractional precipitation was used to isolate the graft copolymer from related homopolymers. PHA content in copolymer samples was between 15 to 30 mol-%. Graft copolymer samples were kept in hydroquinone to prevent post polymerization leading to crosslinking in a day under laboratory atmospheric conditions. Copolymer characterization was performed using GPC and NMR techniques. Thermal analysis of the graft copolymer indicated the decomposition and glass transition temperatures of the PHA and PMMA segments of the graft copolymers. They also showed elongation at break in the range 10 to 21 related to the plasticizer effect of the biopolyester segments.