Several kinds of medicinal plants are used as diuretics in folk medicines and oriental drugs. The diuretic action of water extracts of the ten kinds of crude drugs, such as Pachyma hoelen $R_{UMPHIUS}$ Zea mays L., Akebia quinata $D_{ECAISNE}$, Alisma orientale Juzepezuk, Atractylodes koreana $N_{AKAI}$, phytolacca americana L., Achyranthes japo-nica $N_{AKAI}$, Juncus decipiens $N_{AKAI}$, Prunella asiatica $N_{AKAI}$ and Artemisia capillaris $T_{HUNBERG}$ was examined in mouse and compared with aminophylline as a control the following results were obtained. The urine volume was found to be remarkably increased by the Pachyma hoelen RUMPHIUS, Phytolacca americana L., Prunella asiatica $N_{AKAI}$ and Artemisia capillaris $T_{HUNBERG}$, moderately increased by the Akebia quinata $D_{ECAISNE}$, Achyranthes japonica $N_{AKAI}$ and Juncus decipiens $N_{AKAI}$, and slightly increased by Zea mays $L_{ENNE}$, Alisma orientale $J_{UZFPEZUK}$ and Atractylodes koreana $N_{AKAI}$.