PHOSPHATE solubilizing bacteria are capable to release inorganic phosphate and make it available to plants for growth enhancement. In this study, Serratia marcescens PH1, which has been isolated from tomato plant rhizosphere, has been subjected to different physical and chemical parameters for optimization of its phosphate solubilisation capacity. The best temperature, inoculum percentage, agitation rate, incubation time, and pH value were found to be 30℃, 1.5%, 150rpm, 5 days, and 7-8, respectively. The best carbon source for phosphate solubilisation among 5 different sources, glucose, sucrose, galactose, maltose, and arabinose, was glucose which allows for releasing 797mg/L of P. Besides, casein was the best nitrogen source for phosphorus release (853mg/L) and Ca₃(PO₄)₂ in Pikovskaya medium was the best P source (855mg/L). The key factors affecting P release in the modified Pikovskaya medium were glucose, casein and inoculum percentage. P concentration in the modified Pikovskaya culture medium was 853mg/ml comparing with only 749mg/L in the classical formula. For freeing of P, Serratia marcescens PH1 produces organic acids such as citric, lactic, malic, and benzoic acids. Phosphorus yield was increased gradually with organic acids production till reaching 861mg/ml in 5 days with pH drop to 1.1. pqqC (a gene responsible of PQQ production) gene fragment of approx. 568 bp was successfully amplified in phosphate solubilizing bacteria. Detection of pqq genes is an evidence of gluconic acid production capability. This acid is a well known biocontrol agent. Serratia marcescens PH1 is a strong phosphate solubilizer and we are planning to conduct more wide-scale experiments in pots to optimize the utilization of such bacterium before conducting agricultural applications as a plant growth promoter and a biocontrol agent.