Biopolymers were produced by using Alcaligenes eutrophus microorganisms. Some of substrates such as glucose, sucrose, butyric, pentanoic and propanoic acids used as carbon sources affect the accumulation and composition of biopolymers in the cell. The maximum polymer production (0.97 g/L) was obtained when 2.0 g glucose/100 mL was used as a substrate. Accumulation of polymer in the cell was 28% (wt/wt) when pentanoic acid was used as substrate. Characterization of the biopolymers was carried out by using different spectroscopic and thermal techniques such as FTIR, DSC, H-1 NMR and GC/MS. Glass transition temperature (T-g) and melting temperature (T-m) of the polymers changed between 4.71-11degreesC and 147-179.8degreesC, respectively. Enthalpy of fusion (DeltaH) varied between 43.82 and 96.70 J/g. Biodegradability of PHB was tested in biological medium and in phosphate buffer solution.