Abstract: A new method of quantitative analysis of sodium nitroprusside (SNP) was devel-oped according to the principle of a photodegradation analytical method that has been reported by theauthors previously. After irradiated of solution of SNP under fluorescent lamp, the increase in ab-sorbance at 394 nm belonged to nonlinear kinetics, but the absorbance increment with concentrationwas linear in certain concentration range of SNP. When irradiated for 30 min or 60 min,SNP in solu-tion can be quantitated accurately by ΔA₃₉₄. The standard curve of this method was linear from 50 to1000 mg/L. The within-day and day-to-day precisions(RSD) were 1.9% and 2. 6% respectively,with recoveries of 99.0～100.1%. No interference from small amount of serum protein, stearyl al-cohol,propylene glycol, azone, m-nifedipine, nitrendipine and verapamil was observed. This methodhas been successfully applied to study percutaneous absorption.