Organophosphates (OPs) inhibit cholinesterase and hyperactivate the acetylcholinergic nervous system in the brain, causing motor excitement (e.g., tremor and seizures). However, the mechanism underlying the motor excitement by OPs remains unknown. Here, we performed behavioral and immunohistochemical studies in mice to investigate the tremorgenic mechanism of paraoxon, an active metabolite of parathion. Treating animals with paraoxon (0.15-0.6 mg/kg, i.p.) elicited kinetic tremor in a dose-dependent manner. Expressional analysis of Fos protein, a biomarker of neural excitation, revealed that a tremorgenic dose of paraoxon (0.6 mg/kg) significantly and region-specifically elevated Fos expression in the dorsolateral striatum (dlST) and the inferior olive (IO) among 48 brain regions examined. Moderate to slight increases in Fos expression was also observed in the cerebral cortex, hippocampus, nucleus accumbens, medial striatum, globus pallidus, medial habenula, and solitary nucleus, while these changes were not statistically significant. Paraoxon-induced tremor was inhibited by the nicotinic acetylcholine (nACh) receptor antagonist mecamylamine (MEC), but not affected by the muscarinic acetylcholine receptor antagonist trihexyphenidyl (THP). In addition, paraoxon-induced Fos expression in the dlST and IO was also antagonized by MEC, but not by THP. The present results suggest that OPs elicit kinetic tremor primarily by activating dlST and IO neurons via nACh receptors.