Modulation of monoaminergic systems has been the main stream of treatment for patients with mood disorders. However, recent evidence suggests that the glutamatergic system plays an important role in the pathophysiology of these disorders. This study pharmacologically characterized a structurally novel metabotropic glutamate 5 (mGlu 5 ) receptor negative allosteric modulator, DSR-98776, and evaluated its effect on rodent models of depression and mania. First, DSR-98776 in vitro profile was assessed using intracellular calcium and radioligand binding assays. This compound showed dose-dependent inhibitory activity for mGlu 5 receptors by binding to the same allosteric site as 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a known mGlu 5 inhibitor. The in vivo therapeutic benefits of DSR-98776 were evaluated in common rodent models of depression and mania. In the rat forced swimming test, DSR-98776 (1–3 mg/kg) significantly reduced rats immobility time after treatment for 7 consecutive days, while paroxetine (3 and 10 mg/kg) required administration for 2 consecutive weeks to reduce rats immobility time. In the mouse forced swimming test, acute administration of DSR-98776 (10–30 mg/kg) significantly reduced immobility time. This effect was not influenced by 4-chloro-DL-phenylalanine methyl ester hydrochloride-induced 5-HT depletion. Finally, DSR-98776 (30 mg/kg) significantly decreased methamphetamine/chlordiazepoxide-induced hyperactivity in mice, which reflects this compound antimanic-like effect. These results indicate that DSR-98776 acts as an orally potent antidepressant and antimanic in rodent models and can be a promising therapeutic option for the treatment of a broad range of mood disorders with depressive and manic states.