The invention relates to medicine and veterinary medicine and can be used to prevent and treat iron deficiency anemia and to promote hematopoiesis. The invention discloses, ready to use an injectable composition for the prevention and treatment of iron deficiency anemia an injectable composition for preventing and treating iron deficiency anemia, containing an iron complex with dextran, where iron complex with dextran is an iron (III) and dextranheptonic acid or an iron (III) oligomaltoside as an active ingredient, and a solvent, wherein the composition additionally contains folic acid and a pH adjuster to pH within 6.0-8.0 with the following contents of the components, wt.% : - iron complex with dextran - 0.5-20.0; - folic acid - 0.1-4.0; - pH adjuster- 0.5-6.0; - solvent - the rest; wherein iron complex with dextran contains free iron ions lower than or equal to 0.05%.