C. ambrosioides is a Congolese medicinal plant used in the treatment of several pathologies. This work was initiated to evaluate the analgesic and antipyretic effect of the aqueous extract of leaves of C. ambrosioides. Analgesic effect was evaluated by using the acetic acid-induced writhing, the Tilk Flick test as well as the pain induced by formaldehyde. The results obtained showed that the aqueous extract significantly reduces the number of abdominal writhes (p < 0.05 and p < 0.001), significantly increased the immersion time of the tail (p < 0.05 and p < 0.01) and also significantly decreased the frequency of licking or biting the paw (p < 0.001). This result suggests an analgesic effect of aqueous extract. The fever was induced by subcutaneous administration of a solution of brewer's yeast. The results obtained showed a significant decrease (p < 0.05, p < 0.01 and p < 0.001) of the rectal temperature of the animals treated with the aqueous extract of leaves of C. ambrosioides (400 and 600 mg/kg) compared to control group (saline water). This result suggests an antipyretic effect. Chemical screening revealed the presence of alkaloids, flavones and mucilage. The presence of alkaloids and flavones could explain the analgesic and antipyretic effects attributed to this aqueous extract.