The viscoelastic properties of microbial biodegradable copolymers containing 3-hydroxybutylate (3HB) and 3-hydroxyvalerate (3HV) were investigated as well as the reference homopolymer, poly(3-hydroxybutylate) (PHB), by plotting the first normal stress difference (N-1) versus shear stress (tau(s)) and the storage modulus (G') versus the loss modulus (G "). At low shear rates, the N(1)s of the copolymers were higher than that of PHB, and at high frequencies, the G's of the copolymers were lower than that of PHB. To examine the rheological properties of biodegradable copolymers, we used a modified Cole-Cole plot (N-1 versus tau(s) and G' versus G "). From these plots, we found that the elastic behavior from steady shear experiment is closely related to that of the dynamic oscillatory experiments for the biodegradable copolymer.