The effect of several chosen admixtures (Al3+, Cu2+, Fe2+, Mg2+, Mn2+, Na+ and urea) on crystallization of ammonium sulphate was studied. These admixtures rise the metastable zone width change the nucleation order, affect the overall growth rate as well as the growth rate of individual faces and in this way they change the crystal shape of ammonium sulphate. An explanation of these effects is suggested.