The effect of feed mixture supplementation with MgCl2 on alimentary tract microflora, haematological markers, and selected parameters of reproductive performance of sows was investigated. The animals were divided into control group (K) and two experimental groups (E1 and E2). The sows from the experimental groups were receiving 1 g of MgCl2 6H20/100 kg b.w./day, which constituted 120 mg of pure magnesium, administered in a small portion of a feed mixture. The sows from group E1 were receiving MgCl2 every day for 30 d, whereas sows from group E2 for 60 d. A significant decrease in the count of