The biological effects of poly(ethylene glycol)(PEG), neutral water soluble polyether, on the microbial Poly( β-hydroxyalkanoates)(PHAs) was investigated. Cell viability, polymer repeat unit compositions, and molecular weights of PHAs cultivated by Pseudomonas oleovorans and Pseudomonas putida microorganisms were examined using two-stage batch culture fermentation. Sodium octanoate and Medium E* were used as carbon source and culture medium, respectively. It was discovered that PEG can function to control the molecular weight of product as well as cell productivity from both microorganisms. However, PEG has no notable effect on the molar compositions of polymer biosynthesized.