In the present study, we investigated the role of phosphorylated calcium/calmodulin-dependent protein kinase-II (pCaMK-II) in nociceptive processing at the spinal and supraspinal levels in the substance P (SP)-induced mouse pain model. In the immunoblot assay, intrathecal (i.t.) injection with SP increased the pCaMK-II level in the spinal cord, and an immunohistochemical study showed that the increase of pCaMK-II immunoreactivity mainly occurred in the laminae I and II areas of the spinal dorsal horn. At the supraspinal level, pCaMK-II was increased in the hippocampus and hypothalamus by i.t. SP injection, and an increase of pCaMK-II immunoreactivity mainly occurred in the pyramidal cells and the stratum lucidum/radiatum layer of the CA3 region of hippocampus and paraventricular nucleus of the hypothalamus. Moreover, pCaMK-II immunoreactivity in the locus coelureus of the brain stem was also increased. The nociceptive behavior induced by SP administered either i.t. or intracerebroventricularly (i.c.v.) was attenuated by KN-93 (a CaMK-II inhibitor). Our results suggest that pCaMK-II located at both spinal cord and supraspinal levels is an important regulator during the nociceptive processes induced by SP administered i.t.