Abstract: Objective: To develop a fast and accurate live bacteria fluorescent quantitative detection method applied in the viable count of Lactobacillus paracasei in bacterial powder. Methods: Specific primers were designed according to Phenyl alanine- tRNA synthetase alpha subunit gene( phe S) of L.paracasei N1115. Propidium monoazide( PMA) was used to suppress dead bacteria DNA amplification,and then the q PCR method was used to detect bacteria powder in the number of live bacteria N1115. Results: Specific and verified primers of L.paracasei N1115 were: C15 F,C15R. The thermal damage time of L.paracasei N1115 was 8 min in the 90 ℃ water bath. PMA could obviously control the amplification of dead L.paracasei N1115. The way of PMA- q PCR could detect the number of living L.paracasei N1115 rapidly and accurately.Conclusion: A PMA- q PCR assay had been developed for rapid and accurate detection of viable L.paracasei N1115.