Extended Huckel Calculation of cis-and trans-dichloro diammine platinum(II), dichloroethylene diamine platinum(II) and their N-mono, di, tri and tetra-methylated or ethylated ones were carried out to investigate their anticancer activity. It was found that the net charge of two chlorine atoms in cis-isomers are greater than those in trans-ones and Pt-Cl bond energies of the former are less than that of the latter, indicating that Pt-Cl bond in cis-isomers has greater ionic character than that in trans-ones and Cl atoms in the former are easier to dissociated as Cl- than those in the latter. Also, the values of $b_{2g}-b_{1g}$ energy difference, ${Delta}_1$ were found to be greater in cis-isomers than in trans-one without exceptions. For the substitution of methyl for H atom in ammine and ethylenediamine Pt-Cl bond strength shows the tendency to increase with increasing in number of methyl group. Accordingly, We believe that two Cl atoms in $PtLCl_2$-complexes (L: NH$_3$, en) are dissociated in the first step of the action of anticancer