Additions of urea were found to increase the yield of nickel sulfide formation from acidic solutions of thioacetamide. Two precipitation mechanisms were identified : hydrolysis and direct reaction between nickel and thioacetamide. Hydrolysis-controlled precipitation is evident with low initial pH. The direct reaction is dominant at high initial pH. Nucleation proceeds by a direct reaction between nickel and thioacetamide. The role of urea in precipitation of nickel was found to be twofold. Urea increases the rate of thioacetamide decomposition, thus increasing the concentration of H 2 S form. Secondly, decomposition increases the pH of the solution, which in turn increases the relative concentration of S = ions. Agglomeration of particles was more evident in the powders obtained in the presence of urea.