Platelet-derived growth factor (PDGF) is a major mitogen of many messenchymal original cells. With promising potential, PDGF has been considered as an emerging recombinant product which is targeted to pharmaceutical applications. Testing biological activity is an essential step in PDGF manufacturing. There are in vitro assay which based on PDGF function of stimulating fibrolast cell proliferation and in vivo assay which shows PDGF capability in healing wound. The former assay serves many advantages, such as saving time, expenditure, and scale of experiments. Several PDGF in vitro assays have been used in some scientific publications. While the PDGF manufacturing asks for a stable, specific and authentic bioassay, those published bioassays differ from each others in some parameters such as: synchronization methods, PDGF-treating time, etc. To provide scientific base for selecting and using an in vitro bioassay in PDGF manufacturing in Vietnam, this paper presented the results of evaluation and optimization of PDGF in vitro bioassay. The results demontrated a stable and sensitive PDGF bioassay (%CV<15%) in which 5×103 initial seeding cells per well was used without sychronization, following by 36 hours PDGF-treated in FBS-free medium.