In this research, porous membranes of a biodegradable polymer, poly(hydroxybutyrate), were synthesized and the surfaces of which were modified by plasma-induced polymerization so as to engender functionality to the membranes. Chloroform and ethanol were used as the solvent and nonsolvents, respectively, for membrane formation by the immersion precipitation method. Phase diagram of the ethanol-chloroform-PHB system was constructed; thereby appropriate dope composition was selected. Membranes with different structures were then prepared by changing the dope preparation temperature. The porous structure, crystalline character, mechanical strength, and water wettibility of the formed membranes were studied to understand the relationship between these properties and the membrane formation process. Plasma-induced polymerization method was employed to graft poly(acrylic acid) on the membrane surface. Various variables, viz., plasma treatment time, plasma power, grating reaction time, and monomer concentration were investigated and the largest grafting yield was found to be 0.48 mg/cm2 under optimal conditions.