Abstract: A simple selective spectrophotometry has been developed for determination of molybdenum in the presence of tungsten based on the difference of polymeric behavior and complex ability. In the present paper, it is demonstrated how increase difference of solutional state between molybdenum and tungsten. It has been found that the method do not affect the absorbance of complex by forming molybdenum with bromopyrogallol red (BPR) but the complex of tungsten would almost become to fide.The method was applied to determine the micro amount of molybdenum in the tool steel with Satisfactory results.