Stability of Y(III), La(III), Ce(IIl), Pr(III),Nd(III), Sm(III), Gd(III), Dy(Ill) and Th(IV) complexes of Creatine was studied at 30°C in 10%, 20%, 30%, 40%, 50%, 60% v/v dioxane-water mixtures and ionic strength was maintained as 0.2M (NaClO-i). Titration data was obtained on the basis of Irving-Rossotti technique and data was pruned with computer program PKAS & BEST. Species distribution plots are developed using program SPEPLOT. The active forms of species observed were LH2, LH+, L, ML, ML? and ML(OH)3. The effects of systematic errors on stability constants are studied using concept of modeling. The order for these effects is: dissolved carbon dioxide > alkali > acid > ligand > metal. The stability of inner transition metal -creatine complexes has increased with increasing dioxane content in mixtures. The change in stability constants with change in dielectric constant of medium is explained on the basis of cation solvating nature of cosolvent, specific solvent-water interaction, specific interaction of cosolvent with solute, electrostatic and non-electrostatic effects.