Abstract The ethyl acetate, n hexane and methanol extracts of six cyanobacterial species isolated from paddy fields in Egypt were assessed for their antimicrobial activity, using disc diffusion method. Oscillatoria acuminata, Oscillatoria amphigranulata and Spirulina platensis methanolic extracts showed the highest inhibition zones. Minimum inhibitory concentration of O. amphigranulata extract recorded lower values using agar streak dilution method. O. acuminata methanolic extract exhibited the highest antioxidant activity (6.58 and 34.60 % using DPPH (2, 2- diphenyl-1- picrylhydrazyl) and ABTS+ (2, 2-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) methods, respectively, followed by O. amphigranulata then S. platensis. Similarly, O. acuminata methanolic extract showed very strong cytotoxicity activity against HepG2 and HCT-116 cell lines and strong activity with MCF-7 cell lines. O. amphigranulata extract showed strong cytotoxicity for HepG2 and HCT-116 as well as moderate cytotoxicity for MCF-7 cell line. Whereas, S. platensis extract exhibited moderate cytotoxicity for all cell lines. Results of gas chromatography/mass spectroscopy analysis pointed out that the potential activity of these cyanobacterial extracts might be attributed to a synergistic effect between their pronounced contents of fatty acids, alkaloids, phytol, hydrocarbons, phenolics and phthalates, especially fatty acids. We recommend cyanobacteria as a rich source of natural products with potent pharmacological and medical applications.