10.22376/ijpbs.2019.10.1.p1-12 Volume 4 Issue 4 2013 (October - December) Cyanobacteria produce bioactive compounds including plant growth regulators that influence the physiological and biochemical profile of inoculated plants. The objective of the present investigation was to study the effect of different cyanobacterial species viz. lessThan i greaterThan Nostoc commune, Anabaena flos-acquae lessThan /i greaterThan and lessThan i greaterThan Westiellopsis lessThan /i greaterThan sp. on growth parameters, photosynthetic activity and antioxidant system of flax ( lessThan i greaterThan Linum usitatissimum lessThan /i greaterThan L.), a recently promoted medicinal plant. Seeds presoaked in the culture extract of these cyanobacterial species enhanced the germination percentage, vegetative growth, chlorophyll content, as well as stimulated the antioxidant system (carotenoid content, peroxidase enzyme and catalase enzyme activity) of the plant and these effects were statistically proved significant. In all the treatments, the germination of flax seeds was faster compared to the control regardless of species employed. 10% extracts of all the selected species was found to be the best for augmenting growth characteristics and antioxidant system. NARESH .L , ALEX B. K. AND KOSHY E.P. Flax, Cyanobacteria, Antioxidant system, Photosynthetic activity 446-455