Pyrenacantha staudtii and Trichilia monadelpha are herbal plants used indiscriminately to treat malaria by local people in Nigeria. Hence the need to examine the effects of these plants on the visceral organs of mice in order to determine their safety use. Crude aqueous extracts of the plants were prepared. Different concentrations such as 500mg/Kg, 800mg/Kg 1000mg/Kg, 2000mg/Kg and 4000mg/Kg of the extracts were separately administered to mice in different groups. After 24h post-administration of the extracts, the mice were sacrificed to examine the histology of their visceral organs. No mortality was recorded among the treated mice 24h post-administration of the extracts. There was no lesion on the lung and heart tissues of the treated mice. The extracts of P. staudtii caused necrosis in the liver and kidney tissues at high concentration. But no necrosis was observed in the liver and kidney tissues of mice administered with T. monadelpha extract. Generally, there were cellular infiltrations in the liver and kidney tissues of the mice administered with the extracts of both P. staudtii and T. monadelpha. No lesion was seen in the tissues of untreated mice. Both P. staudtii and T. monadelpha appeared to be toxic at high concentration. Indiscriminate use of these plants without standard measurement should be discouraged.