Objective:To assess the anticancer activity of eight cyanobacterial hydrophilic extracts on Ehrlich ascites carcinoma cell line.Methods:The cyanobacterial strains used in the investigation were collected from diverse habitats in Egypt.The initial cytotoxicity test of cyanobacterial hydrophilic extracts was carried out by MTT assay.The in vitro anticancer activity of the four most active extracts was performed on MCF-7 cells using sulforhodamine B assay.Morphological and molecular techniques were used to characterise identity of the isolate from which the most potent cytotoxic extract was obtained.Results:Extracts from four cyanobacterial strains had higher cytotoxic activities scoring76.68%,77.70%,76.70%and 74.45%,respectively.A considerable anticancer effect was only detected when the concentrated extracts were used.One cyanobacterial extract gave the highest anticancer activity on human breast adenocarcinoma cell line(57.6%of inhibition)as compared to control.The isolate was best-matched to Cyanothece sp.with sequence resemblance 98%to Cyanothece sp.strain PCC7564 and the phylogenetic analysis confirmed its close identity to the Cyanothece genus.Conclusions:This is the first study to report the anticancer effect of aqueous extracts derived from the unicellular Cyanothece sp.from Egypt and its potential as a plausible candidate for future mass biotechnological applications. Objective: To assess the anticancer activity of eight cyanobacterial urine extracts on Ehrlich ascites carcinoma cell line. Methods: The cyanobacterial strain used in the investigation were collected from diverse habitats in Egypt. The initial cytotoxicity test of cyanobacterial extract was carried out by MTT assay The in vitro anticancer activity of the four most active extracts was performed on MCF-7 cells using sulforhodamine B assay. Morphological and molecular techniques were used to characterize identity of the isolate from which the most potent cytotoxic extract was obtained. Results: Extracts from Four cyanobacterial strains had higher cytotoxic activities scoring 76.68%, 77.70%, 76.70% and 74.45%, respectively. A considerable anticancer effect was only detected when the concentrated extracts were used. One cyanobacterial extract gave the highest anticancer activity on human breast adenocarcinoma cell line (57.6% of inhibition) as compared to control The isolate was best-mat ched to Cyanothece sp. with sequence resemblance 98% to Cyanothece sp. strain PCC7564 and the phylogenetic analysis confirmed its close identity to the Cyanothece genus. Conclusions: This is the first study to report the anticancer effect of aqueous extracts derived from the unicellular Cyanothece sp .from Egypt and its potential as a plausible candidate for future mass biotechnological applications.