Abstract: It was shown that upon addition of sodium dodecyl sulfate (SDS) to solutions of crystal violet (CV) in the same concentration,making a series of solutions with graduation of concentration of SDS,a gradual decrease in absorbance at the abs.max.of CV-monomer and a gradual increase in absorbance at the abs.max.of CV-dimer were observed from the absorption spectra of each of the above mixed solutions measured in the visible spectral region,and serious over-lapping of absorption spectra of CV-monomer and CV-dimer,including changes in the spectral shape were also observed.Resolution of spectra-overlapping and the fitting calculation of various spectral-parameters were done automatically by using the Gaussian multi-peak fitting stored in the software Origin 7.5.It was shown that each of the parameters was related sensitively with the concentration of SDS,and a clear turning point was found from the plotting curve.The value of SDS concentration on the abcissa corresponding to the turning point of the curve was taken as the CMC value.The method of finding the CMC value by the turning point in the curve plotted was reported for the 1st time by the authors.