Rat Leukemia Inhibitory Factor (LIF) is a multifunctional cytokine belonging to the IL-6 family—which includes IL-6, IL-11, oncostatin M (OSM), ciliary neurotrophic factor (CNTF), cardiotrophin-1 (CT-1), cardiotrophin-like cytokine factor 1 (CLCF1), and IL-27—and signals through receptor complexes containing the shared gp130 subunit. In rats (Rattus norvegicus), LIF binds to the LIF receptor (LIFR) in association with gp130, activating JAK/STAT3, MAPK, and PI3K signaling pathways that regulate cell survival, differentiation, immune modulation, and tissue repair. Rat LIF plays important roles in reproductive biology, particularly in embryo implantation and uterine function, as well as in hematopoiesis and neural development. In experimental models, LIF-mediated STAT3 signaling is involved in neuroprotection following brain injury, modulation of inflammatory responses in colitis and lung injury, cardiac remodeling after ischemia, and regulation of tumor growth and fibrosis. Dysregulated LIF expression may contribute to chronic inflammation or pathological tissue remodeling through sustained STAT3 activation. Because rats are widely used in neuroscience, cardiovascular, toxicology, and pharmacology research, characterization of rat LIF supports investigations into IL-6 family cytokine signaling, regenerative mechanisms, inflammatory disease pathways, and development of STAT3-targeted therapeutic strategies relevant to human medicine.