Abstract: In alkaline medium,　a reaction forming a blue product takes place among sodium nitroprusside, phenol and hydroxylamine hydrochloride. The blue produ ct exhibits the maximum absorbance at a wavelength of 690　nm and can be measured by spectrophotometry. So a spectrophotometric method is developed for the dete rmination of sodium nitroprusside in the injection solution of sodium nitroprusside. The linear range of the method is 1.0×10^-5～8.0×10^-5 mol/L,　RSD%=0.57％(n=6). The standard addition recoveries of the real samples ’ analyses are more than 95%. The relative errors between the proposed and the standard methods are -1.2%～0.91%. Cl^-, SO^2-₄, 　HCO^-_{3,　Mg2+ and Ca2+　 don’t show obvious disturbance when their concentrations are respectively 40 times higher than that of sodium nitroprusside. The method is precise and the operation is easy and convenient.}