Biodegradable poly(3-hydroxybutyrate)/graphene oxide (PHB/GO) nanocomposites were prepared successfully via a solution mixing method. Transmission electron microscopy and wide angle X-ray diffraction results indicate that the GO sheets were homogeneously dispersed in the PHB matrix. Effect of GO on the thermal stability, nonisothermal melt crystallization behavior, isothermal melt crystallization kinetics, spherulitic morphology, and crystal structure of PHB in the nanocomposites was investigated in detail with various techniques. The observed decomposition temperature of PHB has been improved dramatically in the PHB/GO nanocomposites relative to neat PHB. Both nonisothermal and isothermal melt crystallization of PHB have also been enhanced significantly in the nanocomposites because of the efficient nucleating agent effect of GO. However, the presence of GO does not change the crystallization mechanism and crystal structure of PHB in the PHB/GO nanocomposites.