It is now established that the process of milk production and its constituents are affected by different physiological factors, including hormones and neurotransmitters. Bombesin (BBS) is a tetradecapeptide that isolated and characterized from the skin of amphibian frog bombina bombina (Jontown et al., 1995). Subsequently, several BBS-like peptides have been identified in mammals consisting of various forms of gastrin-releasing peptide (GRP) and neuromedin B (NMB), together with their distinct receptor subtypes (Jian et al., 1999). Nowadays, they have been found at different parts of the body such as neuron system, gastrointestinal tract and some nucleuoses of hyphothalamus of vertebrates and invertebrates. The bombesin family of peptides are biologically active in the central nervous system and periphery. Bombesin achieves to its functions by starting the secondary messenger of inositol triphosphate (IP3). The effects of bombsin on production and constituents of the milk are not studied yet. The aim of this experiment was to determine whether injections of bombesin increase milk amount and constituents in the cows.