Chemistry Department, Faculty of Science, M. S. University of Baroda, Baroda-390 002 The formation constants of the complexes of the type [CuAL], where A=2,2'-dipyridyl, 1,10-pbenantbroline, 2-(2.'-pyridyl)benzimidazole or 2-(2'-pyridyl)imidazoline and L=acetylacetone or benzylacetone have been determined in dioxan-water (1 : 1 v/v) solutions and µ=0.2 (NaClO4) at 30º. The formation constant values have been determined by graphical method and further refined by using a computer programe. The value of ∆log K (log \(K_{MAL}^{MA}\) -log \(K_{ML}^M\)) is found to be positive in (CuAL) complexes. The fact that ∆log K is positive in Cu(II) complexes, can be explained to be due to repulsion between metal dπ electrons and electron density over L.The study of uv and visible spectra also confirm this concept.