Abstract: A new chromogenic reagent,5-4-N-(p-chloro)-benzylammonium pyridyl-10,15,20-tris(4-N-pyridyl) porphyrin chloride,was use in the spectrophotometric determination of trace amounts of copper.In a phthalate buffer medium of pH 3.2,a coordination complex was formed between the new porphrin reagent and Cu2+ ion with its absorption maximum at the wavelength of 428.0 nm,and mole ratio of 1 to 1.Apparent molar absorptivity(ε428) was found to be 1.9×105L·mol-1·cm-1.Beer′s law was kept within 0.1 mg of Cu2+ in 1 L of solution,in respective to its linear regression equation of A=0.0152+0.31 C(r=0.999 1).The proposed method was applied to the determination of trace amounts of copper in 3 standard samples of environmental water,giving results in consistency with the standard values.