Poly(3-hydroxybutyrate), PHB, is a widely distributed carbon storage polymer among prokaryotes including Rhizobium. Capacities of Rhizobium etli R13 to produce the bioplastic during growth on media with different carbon sources appeared to be specific carbonsource. In fed batch fermentation, R. etli R13 resulted in cell dry weight 6.2 g/L and PHB 51.4%. Gas chromatography-mass spectrometry and gel permeation chromatography analysis revealed that PHB produced from R. etli R13 was solely composed of 3-hydroxybutyric acid and the molecular mass of the purified PHB was 3.4 x 10(5) Da with polydispersity 1.47. Dielectric relaxation of PHB has been studied in the temperature and frequency ranges 300-440 K and 10 kHz-4 MHz, respectively. A clear dielectric alpha and rho-relaxation processes are observed in these studied ranges of temperature and frequency. The first process is due to the dipole relaxation in the crystalline phase of PHB. The second one is due to the space-charge formation or Maxwell-Wagner-polarization. The alpha-relaxation process has been investigated by semiempirical Havriliak-Negami relaxation function. The activation energy (E(a)) and the relaxation time (tau(0)) are calculated using the Arrhenius equation. The dielectric relaxation strength (Delta epsilon) is strongly temperature dependent. The calculated values of E(a) for ac conductivity, ln(sigma), of PHB provide information about the presence of electronic conduction. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 3306-3313, 2011