The equilibrium cocrystallization coefficients D M/CoSO4.7H2O of low amounts (10-3- 10-1%w/w) of M2+ ions (M2+ = {Ni2+, Mg2+, Cu2+, Zn2+, Fe2+, Mn2+, Cd2+, Ca2+}) with CoSO(4)7H2O have been determined with the method of long-time stirring of crushed CoSO(4)7H2O crystals in their saturated solution at 20ºC and compared with coefficients determined by means of the method of isothermal decreasing of supersaturation during 3 ­ 360 hours of stirring. This enabled the time needed to reach equilibrium to be found. It is different for different microcomponents. The determined cocrystallization coefficients are diverse: from <0.008 for Ca2+ to 1.20 for Fe2+. Their dependence on some physicochemical and crystal-chemical properties of both sulfate hydrates (CoSO(4)7H2O and MSO4nH2O) and metal M2+ ions has been discussed. They depend mainly on solubility in water and structure of corresponding sulfate hydrates as well as on radii of M2+ ions. It is possible to calculate cocrystallization coefficients with empirical formula based on determined relationships between some of the considered properties of macrocomponent and microcomponents and D M/CoSO4.7H2O coefficients at the average relative error not exceeding 10%