Swertia japonica Makino has been used as a traditional medicine for a long time in Japan. The aim of this study is to clarify the effect of cultivars, plant age and altitude of production site on swertiamarin content in S. japonica plants. The seedlings of 9 cultivars in the field, 5 cultivars in the field or pot and 3 cultivars in the field or pot were used for experiments 1, 2 and 3, respectively. In experiment 1, the effect of varietal difference on the content of swertiamarin was investigated. The content in 'S-117' and '15-Haya' was higher than that in the other cultivars. In experiment 2, the content of swertiamarin in one-year-old seedlings was compared with that in two-year-old ones. In the case of potted seedlings, the content of swertiamarin in two-year-old seedlings was higher than one-year-old ones in all cultivars except 'S-117'. In comparison between potted seedlings and those in field, however, the content in one-year-old potted ones in some cultivars was the same range or higher than that in two-year-old ones in field. In experiment 3, the content of swertiamarin in 3 cultivars cultivated on the altitude of 1,800 m (Sugadaira, Nagano), 815 m (Komoro, Nagano) and 20 m (Kashiwa, Chiba) was investigated. In field culture, 'Mimaki-2-go' and 'Mimaki-3-go' seedlings grown at Sugadaira showed significantly higher swertiamarin content than those at Komoro. In pot culture, the content in 'Mimaki-2-go' and 'Mimaki-3-go' seedlings grown at Komoro was significantly higher than in the seedlings grown at the other altitudes.