Abstract: Distribution of orexin B immunoreactive neurons and fibers in the central nervous system of pigs was studied by immunohistochemistry. The results showed that orexin B positive neurons and fibers were observed in the hypothalamus, brain stem and spinal cord. In the hypothalamus, orexin B immunoreactive neurons and fibers were found in the the preoptic area, suprachiasmatic nucleus, paraventricular nucleus, periventricular nucleus, dorsomedial hypothalamic nucleus, perifornical nucleus, mammillary nucleus, lateral and posterior hypothalamic areas, and with dense distribution in the perfornical nucleus, zona incerta, dorsomedial nucleus and posterior hypothalamic area and sparse distribution in the preoptic area, lateral hypothalamic area and mammillary nucleus. In the brain stem, orexin B immunoreactive neurons were observed in the locus ceruleus, vestibular nucleus, inferior olivary nucleus, nucleus of solitary tract and nucleus ambiguus. In the spinal cord, orexin B immunoreactive neurons were sparse and distributed in the lamina Ⅳof the dorsal horn of cervical segment of the spinal cord. Furthermore, dense orexin B immunoreactive fibers were found in the diagonal band, septal area and bed nucleus of the stria terminalis. Our results provided the bases for the studies of the physiological functions of orexin B in pigs.