Abstract: Electronic structure of 23 platinum (Ⅱ) complexes of the types of (NH₃)₂Ptx₂, (CH₃NH₂)₂Ptx₂, enPtx₂ and 1,2-(NH₂)₂C₆H₁₀Ptx₂ (X=Cl-,Br^-, I^-,1/2(oxalate)^2-,1/2(malonate)^2-, 1/2(hydroxymalonate)^2-, 1/2(methylmalonate)^2-,1/2(ethylmalonate)^2-,1/2(1,1-cyclobutanedicarboxylate)^2-, SCN^-)have been calculated by CNDO/2-SCF method. Seven regressions are obtained from the calculated electr onic indices according to biological activity. The results show that the toxicity and activity of the complexes are closely related to both the amine and the acid redical ligands. It seems that the toxicity of a Pt complex is decreased when appropriate cyclo-amine and organic acid radical serve as ligands, and a high electron density of N atom increases the activity of the complex.