The present investigation was carried out to evaluate the response of two groups of seaweeds of red sea to prevailing environmental conditions. Total four seaweeds were selected from two groups viz. (i) Red seaweeds (Rhodophyta): Gracilaria salicornia (Gs) and Digenea simplex (Ds); and (ii) Green seaweeds (Chlorophyta): Ulva reticulata (Ur) and Chaetomorpha linum (Cl). The performance of seaweeds was assessed in terms of photosynthetic pigments (Chl a, Chl b, total Chl content, Chl a: b ratio, phycocyanin and phycoerythrin), thiobarbituric acid reactive substances (TBARS), H2O2content, accumulation of osmolytes (proline: Pro and glycine betaine: GB), activities of antioxidant enzymes (superoxide dismutase: SOD; peroxidase: POX; and catalase: CAT), and total protein and carbohydrates. The results show that green seaweeds contain higher level of all the photosynthetic pigments except carotenoids, phycocyanin and phycoerythrin which were higher in red seaweeds. Regarding activities of antioxidant enzymes, red seaweeds show higher activities of POX and CAT except SOD. Concentration of Pro, GB and total protein and carbohydrate were also higher in red seaweeds. Taken together, all the four studied seaweeds show an immense line of variation in their strategy of endurance under similar environmental conditions, but red seaweeds possess higher levels of antioxidant enzymes and osmolytes, thus better adapted to changing climatic conditions.