Crystallization of calcium oxalate (CaOx) is important both medically and industrially. In industrial processes, precipitation of CaOx causes scale formation on heat exchanger. CaOx is also known as kidney stone. Although CaOx is supersaturated in the human urine, CaOx crystallization is prevented by crystallization- inhibitor molecules. In this study, reaction crystallization of CaOx from pure Ca(Cl)2 solution and Na2C2O4 solution were examined in the presence of various additives. The effcets of pH, temperature and additives on CaOx crystallization were investigated. The additives were citric acid, tartaric acid, L-alanin, albumin BSA, albumin egg, L-(-) tryptoptan, DL-lysine, D-threonine, L- methionine, D(+) proline and L-asparagine. Particle size of the products were measured. The average particle size results agree with filtration rate results and SEM photographs. In order to determine the adsorption characteristics of amino acids on the CaOx crystal surfaces, zeta potential measurements were also performed. TG-DTA, FT-IR and XRD analysis were performed to determine the variation in the calcium oxalate forms.