Abstract This study investigated the anticonvulsant activity of a new phthalazine tetrazole derivative, QUAN-0808 (6-(4-chlorophenoxy)-tetrazolo[5,1-a]phthalazine), in the mouse maximal electroshock (MES) seizure model. The neurotoxicity of QUAN-0808 was investigated using the rotarod neurotoxicity test in mice. QUAN-0808 exhibited higher activity (median effective dose, ED50=6.8mg/ kg) and lower neurotoxicity (median toxic dose, TD50=456.4mg/kg), resulting in a higher protective index (PI=67.1) compared with carbamazepine (PI=6.4). In addition, QUAN-0808 exhibited significant oral anticonvulsant activity (ED50=24mg/kg) against MES-induced seizure with low neurotoxicity (TD50>4500mg/kg) in mice, resulting in a PI value of more than 187.5. QUAN-0808 was also tested in chemically induced animal models of seizure (pentylenetetrazole [PTZ], isoniazid [ISO], thiosemicarbazide [THIO] and 3-mercaptopropionic acid [3-MP]) to further investigate the anticonvulsant activity; QUAN-0808 produced significant anticonvulsant activity against seizures induced by ISO, THIO and 3-MP.