This experiment was conducted with 126 as-hatched male Arbor Acres chicks (1-d-old, weighing 45.3 ± 0.72 g) to determine the effects of microalgae [MA, containing 29% docosahexaenoic acid (DHA)] on performance, serum composition, carcass trait, antioxidant status, and fatty acid deposition of birds. The birds were allocated randomly to 1 of 3 treatments with 7 replicate pens per treatment (6 birds per pen). The dietary treatments included a control diet [corn-soybean basal diet supplemented with 3% soybean oil (SO), CON], 1% MA diet (basal diet supplemented with 1% MA and 2% SO, 1MA), and 2% MA diet (basal diet supplemented with 2% MA and 1% SO, 2MA). All birds were raised in wire-floored cages. The trial consists of a starter phase from d 1 to 21 and a grower phase from d 22 to 42. Compared with CON, birds supplemented with MA (1MA or 2MA) had greater (P < 0.05) average daily gain, liver percentage (liver weight/body weight), and serum glucose, as well as lower (P < 0.05) feed conversation ratio, abdominal fat percentage (abdominal fat weight/body weight), and total serum cholesterol. Moreover, due to the high concentration of DHA in MA, birds fed MA showed increased (P < 0.05) concentration of eicosapentaenoic acid, DHA, superoxide dismutase, and total antioxidant capacity, as well as decreased (P < 0.05) n-6/n-3 polyunsaturated fatty acid ratio, polyunsaturated fatty acid/saturated fatty acid ratio, and malondialdehyde in the breast and thigh muscle compared with CON. In conclusion, dietary supplementation with 1% or 2% DHA-rich microalgae had positive effects on performance, serum composition, carcass trait, antioxidant status, and fatty acid deposition in birds.