It's no longer news that antioxidant compounds play a vital role in our organisms, as they help neutralize reactive species before they can cause cellular damage responsible for initiating or spreading numerous diseases. For this reason, compounds with antioxidant capacity have been extensively researched. In this scenario, microalgae have been recognized as promising sources of bioactive pigments such as carotenoids, chlorophylls, and phycocyanins, which can be applied to reduce oxidative damage. This bioactive property may occur through different mechanisms and can be evaluated by several methods. Among the existing protocols are in vitro methods, cellular determinations, and protocols involving in vivo evaluations. Each methodology has a specific reaction medium that results in some limitations. In general, for assertive measurements, the chemical characteristics of the evaluated compound need to be considered, since microalgae pigments have both lipophilic and hydrophilic characteristics. Based on this context, this chapter presents a comprehensive description of the most common and recent methods applicable to determining the antioxidant capacity of microalgae carotenoids, chlorophylls, and phycocyanins, including the structural characteristics, bioactivity of the pigments, principles, mechanisms, limitations, and applications of existing methods.