This study is an attempt to investigate the effects of the water extracts of the whole plants of Prunella vulgaris (Labiatae) and Thesii chinense (Santalaceae) on the acute toxicity, the activities on central nervous system and the diuretic action. The acute toxicities shown by $LD_{50}$ were estimated to be more than 3000 mg/kg p.o. and 1,000 mg/kg s.c. in the extracts of Prunellae Herba and Thesii Herba, respectively, in mice. The extracts at a dose of 2,000 mg/kg p.o. did not show any activities on central nervous system, i.e, sedative, analgesic, hypothermic and anticonvulsant actions. The urination in rats was increased by 45.5% and 57.6% when 100mg/kg of each of the extracts were given orally. The results obtained revealed that the water extracts possessed weak diuretic actions without any of central nervous system activities. Furthermore, it is considered that the potassium in the extract may play a role in the diuretic action.