The Indonesian people still empirically use medicinal plants to overcome their diseases or maintain their health. One of the medicinal plants is Cassia siamea Lamk. (claim johar,) used for treatment offevers/malaria and jaundice/hepatitis. A lot of people usually use it for long periods of time. It is preferable for medicinal plants to have no effect rather than toxic effects. Subchronic toxicity test of the infusion of the leaf of Cassia siamea Lamk. have been carried out on 72 female Wistar albino rats for 4 months. The administration of the test materials were orally, every day except Sunday and there were three kinds of difference dosages respectively 25 mg/100 g b.w.; 250 mg/100 gb.w. and 500 mg/100 gb.w. that means equivalent to 5 x; 25 x and 50 x usual dose of man. The control group received water only. The results showed that the infusion of the leaf of Cassia siamea Lamk. administered orally, every day until 4 months, the dose of up to 500 mg/100 g b.w. didn't show toxicological effect on the internal body organs of the test animals such as liver, lung, heart, spleen, kidney and intestine.