The aim ol this study is to search for changing of acid- base balance, Ca⁺⁺, Mg⁺⁺ and P⁺ levels, when MgS0₄ is added to the ration for last penod of pregnancy in cows. Thus, understanding of importance of this material for prophylaxis in parturient paresis. As a material, 18 cows which will have given a birth within 20 and 30 days, have been used. The animals are divided 3 groups (each group include 6 animals). First group, the cows has been used as a control, 11, group animals which will have given a birth within 20 days, has been used. These animals were led with 126 gr MgS0₄ which was added in the ration. III. Group animals which will have given a birth within 1 month . These animals are fed with 126 gr MgSO₄ which was added in the ration. Compare with same samples times have been evaluated of each groups, there is significantly decrease lor HC0₃- (p<0.05) levels between group I and III for 4th and 6th sampled. There is statistically decrease for BE levels( p<0,05. p<0.005) in the group I, grup II and group III for plasma samples which are collected 3^rd, 4^rd, 5^th, 6^th and after to given a birth, There is significantly increase for plasma ICa⁺⁺ level (p<0.05, p<0.005) between group 1 and group II considered for collection of 5th and 6th sampled. Similar result were taken between group I and III (p<0.05, p<0.005) considered for collection of 3^rd, 4^rd, 5^th and 6^th sampled period. Total serum Ca⁺⁺ levels (p<0.05, p<0.005) also show statistically differences between group I and group II for 5^th, 6^th and after to given a birth sampled period, comparasion study show that there-is differences between group I and III collection of 4^rd, 5^th,6^th and after to given a birth sampled period lime. In case of this result, there is significatly decrease for P⁺ (p<0.05)levels between group I and III for 5^th and 6^th sampled during the study. But also there is significatly decrease for K⁺ (p<0.05)levels between group 1 and III for 6th and after to given a birth sampled period time. Magnesium sulphate which is added lo the ration last period of cow pregnancy period, is help to stimulate increasing of plasma TCa⁺⁺ and ICa⁺⁺ levels statisticaly significantly. This result is indicate that parturient paresis could be prevented by adding magnesium sulphate in the ration within the last period of cow pregnancy period.