Sapindus trifoliate is a medium-sized deciduous tree growing wild in south India that belongs to the family Sapindaceae. The pericarp is reported for various medicinal properties. A thick aqueous solution of the pericarp is used for the treatment of hemi crania, hysteria or epilepsy in folklore medicine. As antiepileptic action is due to muscle relaxation we thought of investigating the muscle relaxant action and locomotor activity of aqueous extract of Sapindus trifoliatus (AEST) in swiss albino mice in comparison with that of diazepam. Extract was evaluated for its muscle relaxant action compared with control and standard diazepam using Rotarod and photoactometer. Fifty mice of either sex were taken and divided in to five groups of 10 each. First group was considered as control, second as standard (Diazepam), third, fourth and fifth as test group (with three different doses of AEST). All the drugs were given orally. 100 and 200 mg/kg of AEST significantly reduced the time spent by the animals on revolving rod when compared to control (P<0.01). There was dose dependent increase in muscle relaxation, maximum with 200mg/kg. The spontaneous locomotor activity with three different doses of AEST (50,100 and 200 mg p.o.) showed dose dependent decrease in locomotor activity that is 71.37%, 85.11% and 87.73% respectively when compared to control. The values are highly significant (P<0.000). In conclusion it is observed that Sapindus trifoliatus has muscle relaxant activity.