Abstract: Determination of derivative absorption spectra with conventional or monowavelength UV-VIS spectrophotometer was performed by measuring the absorbances (A) of the sample at different wavelength (λ),and then converting the serial data of A and λ to values of 1st,2nd and 3rd derivative at different wavelength,i.e.the relationships between λ-ΔA/Δλ,λ-Δ2A/Δλ2,and λ-Δ3A/Δλ3 by mathematical calculations,and plotting the respective derivative absorption spectra on a computer with the software EXCEL.By the use of mathematical method and computer technique in combination with spectrophotometry,the function of conventional UV-VIS spectrophotometer was extended to derivative spectrophotometry.