The present experiment was to evaluate the effects of dietary Spirulina (SP) supplementation in growing pigs. A total of 140 pigs [(Landrace × Yorkshire) × Duroc, 25.32 ± 1.36 kg] were randomly distributed to one of four treatments: control, basal diet; treatment 1, basal diet + 0.025% SP; treatment 2, basal diet + 0.050% SP; and treatment 3, basal diet + 0.100% SP. Growing pigs fed 0.050% SP diet had greater (P < 0.05) body weight and fecal Lactobacillus counts compared with pigs fed basal diet. Average daily gain and gain to feed ratio were greater (P < 0.05) in pigs fed 0.050% and 0.100% SP diets as compared with pigs fed basal diet. The apparent total tract digestibility (ATTD) of dry matter (DM) and superoxide dismutase (SOD) activity for pigs fed 0.050% SP diet tended to increase compared with pigs fed basal diet (P < 0.10). Pigs fed 0.025%, 0.050%, and 0.100% SP had a higher (P < 0.05) glutathione peroxidase (GPx) activity than pigs fed basal diet. In conclusion, SP supplementation improved growth performance and ATTD of DM, increased the SOD and GPx activity, and enhanced the fecal Lactobacillus counts in growing pigs.