The effects of the Japanese Kampo (herbal) medicine, Saiko-ka-ryukotsu-borei-to, on spontaneous locomotor activity were studied in mice. Saiko-ka-ryukotsu-borei-to (60 mg, 150 mg and 300 mg/kg/day) was administered for 14 consecutive days in the drinking water and spontaneous locomotor activity was measured for 60 min by a photocell ambulometer. Saiko-ka-ryukotsu-borei-to (60 mg/kg/day) significantly increased the total activity count on the 11th day after the start of administration when compared to vehicle control, whereas failed to significantly affect the activity on the 2nd, 5th, 8th and 14th days. A similar significant increase was also found with a higher dose (150 mg/kg/day) on the 8th day after the start of administration. However, the highest dose (300 mg/kg/day) did not significantly affect locomotor activity throughout the experimental period. We have previously reported that Saiko-ka-ryukotsu-borei-to, at a dose of 60 mg/kg/day, enhances escape attempts assessed by water-wheel rotations in a mouse model of despair, particularly on the 8th, 11th and 14th days after the start of chronic treatment. However, at higher doses (150 and 300 mg/kg/day), Saiko-ka-ryukotsu-borei-to decreases the escaped attempts on the 5th and 8th days after the treatment. It is therefore concluded that the previously reported changes in escape attempts of mice are not associated with the changes in their spontaneous locomotor activity.