In the neostriatum of mammals the neurons and synapses discriminated into several types at the base of their morphological characteristics. A number of neurons are interneuron but some of neurons project efferent fibers to the pallidum, substantia nigra or thalamus. While the neostriatum receive the afferent fibers from cerebral cortex, thalamus, substantia nigra and nucleus raphe dorsalis. The present experiment was performed to identify the corticostriatal synapses in the rat neostriatum after cortical ablation. The results obtained could be summarized as follows: 1) From the rat 2 day after cortical ablation, in the neostriatum some of axon terminals with small round vesicles appeared that synaptic vesicles are variety in size and crowded toward the synaptic thickening. 2) From the rat 3 and 5 day after cortical ablation some of asymmetric synapses with small round vesicles were an increased electron density of the whole axon terminal and the vesicles and the mitochondria formed all ill-defined mass. From these results it may be assumed that the axon terminals of corticostriatal fiber in the rat neostriatum make up the asymmetric axospinous synapses with small round vesicles.