Abstract A series of new 3-[5-substituted phenyl-1,3,4-thiadiazole-2-yl]-2-styryl quinazoline-4(3 H)-ones were synthesized and evaluated for anticonvulsant, sedative–hypnotic and CNS depression activities. After i.p. injection to mice or rat at doses of 30, 100, and 300 mg/kg body weight 2-styryl quinazolin-4(3 H)-ones derivatives were examined in the maximal electroshock (MES) induced seizures and subcutaneous pentylenetetrazole (scPTZ) induced seizure models in mice. Rotorod method was employed to determine the neurotoxicity. Out of 18 compounds only 4a, 4e and 4p showed anticonvulsant activity in one or more test models. All except 4l and 4q exhibited significant sedative–hypnotic activity via actophotometer screen. Forced swim pool method to determine CNS depressant activity resulted in some potent compounds. It can be concluded that synthesized compounds exhibited better sedative–hypnotic and CNS depressant activities than anticonvulsant activity.