Abstract: Background and Objective: Ageratum conyzoides L. (Asteraceae) is nutrient compliant weed used as forage for grazing animals. It is used in the treatment of various ailments such as wounds, diabetes, pneumonia, asthma and stomach upset. This present study investigated the influence of quarrying on the nutritional composition, heavy metals and oxidative stress indices of the leaves, stem and root of Ageratum conyzoides. Materials and Methods: The various parts of Ageratum conyzoides harvested from a quarry site were compared with those harvested from a non-quarry (control) environment. Phytochemicals, proximate, mineral compositions as well as heavy metals, oxidative stress and air pollution tolerance index were investigated using standard analytical methods. Results: The results from this study revealed greater amount of alkaloid, saponins and flavonoids in the leaf, stem and root from the quarry site when compared to the control site. The micromorphological foliar revealed constricted venial and stomatal deformed guard cells on the quarry site when compared to the control. There were increased levels (p<0.05) in ascorbic acid, air pollution tolerance index (APTI) and pH in the samples collected from the quarry site, while percentage relative water and chlorophyll contents significantly decreased (p<0.05) in the quarry site when compared to the control. Conclusion: The results show that quarry mining activities induced biochemical stress and increased health promoting phytochemicals in Ageratum conyzoides.