In recent decades, natural antioxidant alternatives have become a trending topic for replacing artificial antioxidants. Microalgae have been reported to display interesting bioactive properties and their antioxidant activity is one of them. This study aims to evaluate the antioxidant capacity, phytochemical constituents and proximate composition of three microalgae Scenedesmus obliquus, Chlorella vulgaris and Spirulina platensis. The performed preliminary phytochemical analysis of the algae extracts revealed that they contain good amounts of bioactive compounds. The results showed that the highest total antioxidant activity found was (3720.67 mgAAE/100g) in Spirulina platensis, followed by Chlorella vulgaris (2794.80 mgAAE/100g). The lowest activity was noticed for Scenedesmus obliquus (1718.53 mgAAE/100g). As for total phenolic content, Spirulina recorded the highest phenolic content (2238.46 mgGAE/Kg.), followed by Chlorella (710.33mg GAE/Kg.), and then Scenedesmus (511.20 mgGAE/Kg). The total flavonoids content of algal extracts expressed as mgQE/Kg varied from (548.66) for Chlorella vulgaris, (142.23) for Spirulina platensis to (66.56) for Scenedesmus obliquus. The proximate analysis results indicated high values of protein for Spirulina platensis (53.30 % dry wt.) whereas the highest fat, ash and moisture percentages were recorded by Scenedesmus obliquus (15.13, 15.07 and 2.57, respectively).