Interleukin-3 (IL-3) is an interleukin, a type of biological signal (cytokine) that can improve the body's natural response to disease as part of the immune system. It acts by binding to the Interleukin-3 receptor.

IL-3 stimulates the differentiation of multipotent hematopoietic stem cells into myeloid progenitor cells as well as stimulates proliferation of all cells in the myeloid lineage (erythrocytes, thrombocytes, granulocytes, monocytes, and dendritic cells). It is secreted by activated T cells to support growth and differentiation of T cells from the bone marrow in an immune response. Interleukin-3 is a hematopoietic colony-stimulating factor that is capable of supporting the proliferation of a broad range of hematopoietic cell types. Interleukin-3 also has neurotrophic activity .