Recently many investigators have devoted considerable attention to the production and purification of PA for antigens, and the preparation of new synthetic medium (RM medium) have solved to increase the yields of the PA but, the low sensitivity of the PA to detect B. anthracis infections has remained as a problem to be solved. This study was undertaken to evaluate the yields of the PA from culture filtrates of B. anthracis Sterne $34F_2$ strain in modified RM medium in which 10 g/l of $NaHCO_3$ and 10g/l of glucose were replaced by 8 g/l and 5 g/l, and the first purification step of PA from culture broth was used hydroxyapatite. The PA was purified by hydroxyapatite column chromatography, DEAE-Sepharose CL-4B column chromatography and Toyo-pearl gel filtration chromatography. The yield of PA from the modified RM medium, 8.6 mg/l.