Bovine mastitis is an important animal health disease leading to significant economic losses to the dairy industry due to higher treatment cost and culling rate. Massive influx of somatic cells and secretion of inflammatory mediators into udder are the common features in intramammary infection. During inflammation, lipid derived mediators such as prostaglandins are involved in mammary immunity which exerts potent chemokinetic and chemotactic activity on leukocytes. Cyclooxygenase (COX), a key enzyme, plays a vital role in prostaglandin synthesis during inflammation. An increased synthesis of arachidonic acid metabolites and high concentration of COX are observed during mastitis. Nitric oxide (NO), produced from L-arginine by nitric oxide synthase, controls various vital physiological functions of body and it is important in the host defense by destroying microbes. The antimicrobial effect of NO on bacteria is due to peroxynitrite, reactive nitrogen metabolite, derived from oxidation of NO. The macrophage and epithelial cells of mammary gland produce significant amount of nitric oxide that takes part in the inflammatory process. Many workers reported that level of NO in mammary gland secretion increases significantly in subclinical and clinical mastitis.