Microalgae are a potentially valuable source of structurally different and biologically active compounds experiencing pharmaceutical and nutraceutical value.  Here we compared the antioxidant, in vitro antimicrobial activity, and anticancer potential of the widely investigated green microalga Tetradesmus obliquus and the less-studied unicellular species Myrmecia bisecta. Based on our findings, T. obliquus extracts had much more outstanding antioxidant potentials than those of M. bisecta where IC₅₀ values of DPPH˙ and ABTS^˙+ were 16.18 and 23.35 µg.ml^-1 in T. obliquus vs. 20.21 and 26.05 µg.ml^-1 in M. bisecta, respectively. Interestingly, the antibacterial activity of M. bisecta extract against the tested human pathogenic bacterial strains was more powerful than those of T. obliquus, i.e., 45.2% and 25.3% inhibition vs. 32.3% and 14.20% inhibition against Escherichia coli and Staphylococcus aureus, respectively. Both microalgal species showed significant cytotoxic effects against the HepG2 cell line with IC₅₀ values of 36.44 and 40.12 µg.ml^-1 for T. obliquus and M. bisecta, respectively. Also, both of the two microalgal species showed significant cytotoxic effects against the WI-38 cell line with IC₅₀ values of 65.63 and 61.74 µg.ml^-1 for T. obliquus and M. bisecta, respectively. Based on our results, both T. obliquus and Myrmecia bisecta are reasonable candidates for future applications in pharmaceutical manufacturing.