This study investigated the antioxidant system and the growth of marine cyanobacteria, Synechococcus sp., illuminated by white (350–700 nm), red (630 nm), green (530 nm) and blue (450 nm) light-emitting diodes (LEDs) during 8 days of cultivation. We measured dry weight, total lipid concentration, antioxidant enzyme (superoxide dismutase, catalase and glutathione peroxidase) activities, lipid peroxidation and H2O2 levels. In red and green LED light, dry weight and total lipid concentration were significantly higher than under other light spectra. Furthermore, antioxidant enzyme activities were significantly higher in red light than in the other light spectra evaluated. However, the H2O2 level in red light was significantly lower than that found under other light spectra. These results indicated that red LEDs inhibit oxidative stress and enhance antioxidant function in cultured Synechococcus sp.