The interaction of bacillus subtilis proteinase(BSP) and Alizarin Complex (ALC) was investigated by spectrophotometric method in acidic solution(pH 4.20). When BSP was added into ALC, a red color was observed, which indicated the formation of BSP-ALC associated compound. The maximum absorption of the red color coordination compound was obtained at 510 nm. It was found that the red shift of maximum absorption of the complex was 85 nm. According to balance percolation method, molar ratio method and double wavelengh method, the apparent molar absorptivity epsilonB = 6.68 x 10(3) L x mol(-1) x cm(-1). Conditional constants were defined, the maximum binding number n = 10, and the apparent binding constant K = 7. 25 x 10(6) L x mol(-1). It was found that Scatchard model is appropriate in the treatment of data obtained here.