Highly efficient separation and purification of polyhydroxyalkanoates (PHAs) front PHA-containing cell mass is essential to production of the bioplastics from renewable resources in a cost-effective, environmentally friendly way. Based oil selective dissolution of non-PHA cell mass (NPCM) by protons in aqueous solution and crystallization kinetics of PHA biopolymers, a simple process is developed and demonstrated to recover PHAs from cell mass to high purity (> 97 wt %) with high yield (> 95 wt %). The average molecular weight of biopolyesters is controlled, which follows an exponential function of process severity, a combined factor of processing conditions. Compared with conventional chemical treatment such as sequential surfactant and hypochlorite treatment, this new technology substantially reduces the chemical cost for PHA recovery and purification from PHA-containing cell mass.