The fast growing of aquaculture sector increases the needs of natural feed substances such as microalgae. The present study was performed to determine fatty acids composition of brown alga Padina pavonica and address the effects of dietary P. pavonica on growth performance, body composition,bio-somatic indices, blood parameters, antioxidant activity, andoxidative stress marker of redbelly tilapia Coptodon zilli. Redbelly tilapia specimens (3.58 ± 0.02g) were fed with commercial pellets mixed with four concentrations of P. pavonica 2.0, 4.0, 6.0, and 8.0g/ kg for 45 days. This study was performed under farming conditions. The results showed that the oleic acid C18:1(ω9) is the most dominant constituent of fatty acids in P. pavonica as monounsaturated fatty acids.  Compared to the other groups, Σ MUFAs showed the maximum percentage. At the end of the trial, a highly significant difference was detected between groups in terms of growth performance, body composition, blood indices and somatic indices. In addition, between groups, a highly significant difference (P≤0.05) was recorded concerning MDA, SOD and GSH, while no significant difference (P> 0.05) was shown by CAT enzyme. Generally, the highest results were recorded with concentrations (6.0 and 8.0g/ kg) of P. pavonica diets, as compared to their control.