Macroscopic algae can be found in large open ponds or harvested from the sea. Macro algae includes three distinct groups based on colour: green, brown and red. They are unique in containing secondary metabolites that can be extracted and used for various purposes. This review examines the antimicrobial properties (bacteria, viruses and fungi) of macro algae and its extracts to improve poultry health and performance. This includes body weight gain, feed conversion efficiency and carcass yield improvements in broilers and egg weight and shell quality in layers. As an example, in one study, 35-day body weight of broilers was increased 7.6% with the inclusion of 0.5% Undaria pinnatifida (brown macroalgae) to the diet. The investigations discussed show the diversity of the species available and broad scope where research has been done and the potential for the future.