Microalgae are rich in high protein content that enhances their nutritional and therapeutic benefits in addition to their ability for high mass production. Therefore, the present study was designed to reveal the biological efficiency of the natural proteins isolated form Dunaliella salina, Scenedesmus obliquus and Spirulina platensis. During the current study, it was found that the highest protein content was noticed in S. platensis (48.44%) followed by D. salina (31.75%) then S. obliquus (28.56%). The protein content decreased upon applying some stress conditions on S. platensis and S. obliquus. The electrophoretic detection of the proteins isolated from the microalgal species showed that the vegetative and stressed S. obliquus were physiologically similar to S. platensis by 42.11 and 57.14%, respectively. D. salina was similar to S. platensis by 46.15%. As compared to the vegetative S. obliquus, the stressed S. obliquus and D. salina were similar to 30.77 and 33.33%, respectively. The D. salina was similar to the stressed S. obliquus by 57.14%. The protein pattern was electrophoretically represented by 10 denatured bands in S. platensis, 9 bands in the vegetative S. obliquus, 4 bands in the stressed S. obliquus and 3 bands in D. salina. There was one common band identified in all microalgal species at relative mobility (Rf) 0.95 (Molecular weight (Mwt) 5.27 KDa). There were 5 characteristic (unique) bands identified in the vegetative S. obliquus at Rfs 0.07, 0.17, 0.50, 0.58 and 0.86 (Mwts 214.68, 137.74, 42.37, 30.18 and 12.44 KDa, respectively). The amino acids that were analyzed in the isolated protein hydrolysate showed that 15 amino acids were noticed in S. platensis and S. obliquus. While in D. salina, 17 amino acids were identified. Glutamic acid was the most predominant amino acid and exhibited the highest percentages in D. salina, S. obliquus and S. platensis (4.96%, 3.3% and 7.58%, respectively). Additionally, the in-vitro studies on the isolated proteins showed that the D. salina protein exhibited the highest antioxidant activity at a dose of 100 μg/ml (308.78%) followed by the S. platensis and S. obliquus proteins (140.81% and 124.49%, respectively). Furthermore, D. salina and S. obliquus showed moderate anticholinesterase activity (34% and 36%, respectively). Therefore, microalgal proteins might be used as therapeutic antioxidants and might be used in combination with treatments of Alzhiemer's disease (AD).