Recent research shows an inverse relationship between dietary intake of antioxidant-rich foods and the incidence of human diseases. Since synthetic antioxidant compounds are suspected to be carcinogenic, the search to replace them with natural antioxidants has become a severe action in pharmaceutical research today. In this context, microalgae are wealthy sources of pharmacologically active metabolites with antineoplastic, antitumor, and antimicrobial properties. A microalga such as Chlorella vulgaris, which has active ingredients rich in natural antioxidants in nature, gains excellent importance in this context. Previous studies have reported that C. vulgaris contains a wide variety of bioactive secondary metabolites such as flavonoids and phenolics with antioxidant activity. The first antibacterial studies on Chlorella were made in 1944 by Pratt et al. in his work. They reported that Chlorella has an antibacterial content, which they call Chlorellin. Apart from all these studies, other different effects of Chlorella, such as relieving fatigue, deactivating toxic substances by disrupting their structure, and removing heavy metals from the body, have been investigated in various studies. These properties have made using different Chlorella microalgae as a food supplement popular in recent years. The most popular foods and beverages, such as gluten-free bread and smoothies, promise low fat, high protein, and antioxidant content. In this study, studies on the biological activity of Chlorella will be compiled.