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.

IL-3 stimulates the proliferation of hematopoietic pluripotent progenitor cells. It is secreted by activated T cells to support growth and differentiation of T cells from the bone marrow in an immune response. The human IL-3 gene encodes a protein 152 amino acids long, and the naturally occurring IL-3 is glycosylated. The human IL-3 gene is located on chromosome 5, only 9 kilobases from the GM-CSF gene, and its function is quite similar to GM-CSF.