A series of triazolo[4,3-a]tetrahydrobenzo(b)thieno[3,2-e]pyrimidine-5(4H)-ones (12a-n) were synthesized and evaluated for CNS depressant, skeletal muscle relaxant and anticonvulsant activities by photoactometer, Rotarod and pentylenetetrazole induced the convulsions method respectively in Swiss albino mice. Diazepam was used as standard drug. The five derivatives 12b, 12c, 12d, 12i and 12m showed the CNS depressant and skeletal muscle relaxant activities comparable to those of diazepam at a dose of 5mg/kg. These derivatives also exhibited good activity when tested for anticonvulsant activity in mice at different dose levels. The ED(50) values for these derivatives are in the range of 4.40-9.33 mg/kg.