The genusCoccolobais widely used in traditional folk medicine, but few scientific data exist for this genus. The goal of this study was to characterise the chemical composition and antioxidant activities ofC. alnifolialeaf extracts usingin vitroandin vivoassays. Six extracts were obtained: hexane (HE), chloroform (CE), ethanol (EE), methanol (ME), water end extract (WEE), and water extract (WE). Thin-layer chromatography (TLC) analysis showed the presence of phenols, saponins, terpenes, and flavonoids.In vitroassays demonstrated substantial antioxidant potential, especially for polar extracts (EE, ME, WEE, and WE). Moreover, no toxic effects were observed on mammalian cell lines for most of the extracts at the concentrations evaluated. The nematodeCaenorhabditis eleganswas also used as anin vivomodel for testing antioxidant potential. The EE and WE were chosen, based on previously obtained results. It was observed that neither the EE nor the WE had any toxic effect onC. elegansdevelopment. Additionally, the antioxidant potential was evaluated usingtert-butyl hydroperoxide as a stressor agent. The EE increased the life span ofC. elegansby 28% compared to that of the control, and the WE increased the range to 39.2-41.3%. High-performance liquid chromatography (HPLC-DAD) showed the presence of gallic acid,p-coumaric acid, and vitexin in the WE. Therefore,in vitroandin vivodata demonstrated the antioxidant potential ofC. alnifoliaextracts and their possible biotechnological applications.