The present manuscript includes study of composition and stability constants of mixed ligand complexes of Cd (II) ion with tryptophan and some bicarboxylic acids (Tartaric, Succinic, Maleic, Malonic and Malic acid) voltammetrically. In each case the reduction of the Cd (II) ion is found reversible and diffusion-controlled, involving two electrons in each case. Deford and Hume's method is used to calculate the stepwise formation constants of simple systems while the stability constants of mixed complexes i.e. MXY, MXY₂ and MX₂Y have been evaluated by the method of Schaap and McMasters. With the help of stability constants of these complexes statistical and electrostatic effects have been investigated.