Objective: To understand the postnatal development of the substance P distribution in striatum and globus pallidus in rat brain. Methods: The postnatal development of substance P distribution in the striatum and globus pallidus were studied with the immunocytochemical ABC method after examining serial coronal section s from P01 to 360 rat brain. Results: Substance P, which were immunoreactivity fibers at dorsalventral direction, was mainly distributed in the central and caudate parts of the striatum, most was located at the marginal division of the striatum. There was a little amount of SP fiber in the inner part of globus pallidus and outer dorsal part of caudate-putamen. The postnatal development of substance P distribution in the striatum was as follow: The SPimmunoreactive fibers were only present in the marginal division (MrD). at birth (P01), whereae as globus pallidus(GP) displaying substance P immunoreactivity in its medial border by about postnatal day 10. Sp-immunoreactive fibers appeared first along the lateral part of the caudate-putamen on postnatal day 30. After psotnatal day 30, the distribution of substance P in the striaturn was the same as adult rat. Conclusion: Substance P distributes nonuniformly in the striatum and globus pallidus.The postnatal development of this neurotransmitter has significant difference with other neurotransmitters in the brain.