Ferrous sulphate monohydrate  is the chemical compound with the formula FeSO4, known since ancient times as copperas. It is most commonly encountered as the blue-green heptahydrate.

Used as a feed additive iron fortifier, and also as pesticide in agriculture,  to prevent and control wheat smut, apple and pear scab, fruit rot disease. Used as a nutritional supplement, such as iron strong agent, fruit and vegetable chromogenic agent.

Ferrous Sulphate monohydrate is sometimes added to the cooling water flowing through the brass tubes of a turbine condenser. It forms a corrosion-resistant, protective coating on the inside of the tube. It has been applied for the purification of water by flocculation and for phosphate removal in municipal and industrial sewage treatment plants to prevent eutrophication of surface water bodies.