The palladium(II) and platinum(II) complexes(where, $([M(L)_2X_2]$, M=Pd(II), Pt(II); L=isoxazole(isox), 3,5-dimethylisoxazole(3,5-diMeisox), 3-methyl, 5-phenylisoxazole(3-Me, 5-Ph-isox), and 4-amino-3,5-dimethylisoxazole (4-ADI); X=Cl, Br) with isoxazole and its derivatives were investigated on antitumor activity by MM2 and EHMO calculation. Because for all the complexes the ${sigma}MO$ energy level $(E_{{sigma}(M-X)})$ between $d_x^{2-}_y^2$ orbital of central metal and px orbital of halogen atom is less than ${sigma}MO$ energy level $(E_{{sigma}(M-N)})$ between $d_x^{2-}_y^2$ orbital of central metal and px orbital of N atom, without exception. And judging, from the lower $(E_{'{o}(m-x)})$ value in trans, the bonding strength was found to be weaker in trans isomer than in cis. For the Pd(II) and Pt(II) complexes which have planar ligands, it was shown that for all the complexes dissociation of X-atom in the Pd(II) complexes is easier than that of X-atom in the Pt(II) complexes in both cis- and trans-complexes. Therefore it suggests that the easier dissociation of $X^-$ ion has some relations with antitumor activity, and a linear equation with correlation coefficient of 0.96 was found between ${Delta}E_{{sigma}(N-X)}(E_{{sigma}(M-N)}-E_{{sigma}(M-X)})$ and inhibitory activity coefficient, logIA.