According to the process stated in the ”CFR Microbiological turbidimetric Method, 1981”, the highly purified and frequently used antibiotic raw materials, such as Tetracycline HCl, Oxytetracycline HCl, and Doxycycline HCl were assayed against USP Reference .Standards respectively as secondary, standards and planned to supply domestic pharmaceutical makers for the basis of quality control. The results showed that Tetracycline HCl is 988 μg/mg, Oxytetracycline HCl is 935 μg/mg, and Doxycycline HCl is 850 μg/mg.