The crude ethanolic extract of the leaves of Ageratum conyzoides Linn. (Family: Asteraceae) was evaluated for its possible anti-inflammatory activity as well as total flavonoids and tannins content growing in Bangladesh. The anti-inflammatory activity was studied using carrageenan and histamine-induced rat paw edema test at different doses (200 and 400 mg/kg body weight) of the ethanol extract. At the dose of 400 mg/kg body weight, the extract showed a significant anti-inflammatory activity both in the carrageenan and histamine-induced oedema test models in rats showing 59.15% and 57.76% reduction in the paw volume comparable (P<0.01) to that produced by the standard drug indomethacin (61.27% and 63.35%) at 4h respectively. The percentage inhibition of the oedema paw volume by the 400 mg/kg body weight of the extract was also statistically significant (P<0.05; P<0.01) compared favorably with the indomethacin treated animals at 1, 2 and 3 h in both models. The total flavonoids and tannins content were calculated as quite high in ethanolic extract (281.88 mg/g of quercetin equivalent and 86.47 mg of gallic acid equivalent respectively). Acute toxicity test showed that the plant might be safe for pharmacological uses. Therefore, the obtained results tend to suggest the acute anti-inflammatory activity as well as total flavonoids and tannins content from the ethanolic extract of the leaves of Ageratum conyzoides and thus provide the scientific basis for the traditional uses of this plant as a remedy for pain and inflammations.