Whole-cell patch-clamp recordings were made from striatal ChINs in young-adult mice (P40-51) brain slices. ChINs were voltage-clamped at −60 mV. We used transgenic mice which expressing channelrhodopsin-2 in the striatal MSNs to selectively stimulate these neurons. Light stimulation evoked GABA_A receptor-mediated inhibitory postsynaptic currents (IPSCs) in the presence of glutamate and glycine receptor antagonists. A muscarinic acetylcholine receptor agonist, carbachol, inhibited IPSCs (1 μM: by 33.2 ± 4.4%, n = 9). To examine the changes in GABA release probability, we calculated coefficient of variation (CV), an index of change in release probability before and after application of 1 μM carbachol. Carbachol significantly increased CV from 0.21 ± 0.02 to 0.27 ± 0., suggesting that GABA release probability was changed by carbachol. The inhibitory effect of 1 μM carbachol was reduced to 0.22 ± 4.2% in the presence of pirenzepine, a selective M1 receptor antagonist (n = 6). However, pre-application of a selective M2 receptor antagonist, AF-DX 116 100 nM, did not reduce the inhibitory effect of carbachol (by 40.8 ± 5.0%, n = 8). These results suggest that activation of presynaptic M1 receptor inhibits GABA release from MSNs onto ChINs.