Polyhydroxyalkanoate (PHA) is a biopolymer synthesized by some microorganisms as a carbon and energy storage material under limited nutrient sources, but in excess carbon supply. The PHA is known for its biocompatibility and biodegradability, with amenable physical properties, which can be tailor made into useful material for medical applications such as heart valve, pericardial patches, vascular graft and drug delivery system. Despite the advancement of PHA incorporation as a drug carrier, there is still limited understanding on the potential application of PHA polymer as adjuvant in delivering vaccine or inactivated whole-cell vaccine. This study explored the application of PHA microparticle as adjuvant in treating Pasteurella pneumonia, a bovine respiratory disease. The PHA was synthesized via bacterial fermentation and was fabricated into microparticle through solvent evaporation method. Optimizations in terms of the type of organic solvent used, the concentrations of polymer, and surfactant were carried out. Later, formalin-inactivated Pasteurella multocida B:2 cells were incorporated to the PHA microparticle using solvent evaporation technique. Characterization of PHA microparticles suggested sizes, ranging from 300 to 600 nm, with zeta potential values of -0.07 to 0.03 mV and polydispersity index of 0.28 to 0.41. The PHA-whole-cell adjuvant matrix were heterogenous in shape, with poly(3-hydroxybutyrate) [P(3HB] forming smoother and more spherical shape as compared to poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HBco-4HB)]. The PHA-whole-cell matrix did not exhibit cytotoxicity on rat skeletal muscle (L6) cells. After 72 hours treatment, more than 84% cell viability was observed at 100 mg/ mL concentration.