The dorsal striatum, which contains the dorsomedial striatum (DMS) and dorsolateral striatum (DLS), integrates the performance of discrimination learning. The dorsal striatum receives excitatory inputs from many cortical areas and the thalamic nuclei and projects to the output nuclei through two major pathways composed of the direct and indirect pathways. We found that the DLS-derived striatopallidal pathway plays an essential role in the execution of conditional discrimination, showing its contribution to the control of selection accuracy of learned motor responses (Nishizawa et al., 2012). However the mechanism by which the DMS-derived striatopallidal pathway remains unclear. To determine the behavioral processes through the DMS striatopallidal pathway, we induced selective elimination of this pathway by injecting the recombinant immunotoxin into the DMS of transgenic rats that expressed human interleukin-2 receptor α-subunit under the control of dopamine D2 receptor gene promoter. Then we examined the behavioral consequence of striatopallidal elimination on the performance of discrimination task. In these rats, the correct response ratio was significantly reduced on post-operative days 7 to 10. Moreover, to validate perseverative behavior, we classified all trials in the auditory discrimination task, after a correct response had been made, based on the stimulus repeated or changed in a subsequent trial. The error probability, defined as the ratio of the error response number to the correct response number, was calculated at the early phase comprising the first three sessions. The error probability was significantly higher in the transgenic rats for the changed stimulus, whereas the error probability for the repeated stimulus was not changed. Our results suggest that the DMS striatopallidal pathway regulates the performance of conditional discrimination through controlling the perseverative response.