An experiment was performed to study the effects of a low inclusion level of Chlorella vulgaris (CV) biomass in broiler diets on performance, immune response related to inflammatory status, and the intestinal histomorphology. The study was performed with 120 Ross 308 male broiler chickens from 0−35 days of age. The broilers were housed in 12 floor pens (1.5 m2) bedded with wood shavings. The broilers received a three phase diet program, either with 0.8% CV biomass (CV) or without CV (CON). Each diet program was replicated in six pens. The final body weight increased (p = 0.053), and the feed conversion ratio (FCR), corrected for body weight, was reduced (p = 0.02) in birds fed CV compared to birds fed CON. In addition, decreased haptoglobins (p = 0.02) and interleukin-13 (p < 0.01) responses were observed during the grower phase of birds fed CV compared to the birds fed CON. A strong correlation (r = 0.82, p < 0.01) was observed between haptoglobin response and FCR. Histomorphology parameters of the jejunum were not different between the groups. It was concluded that the inclusion of 0.8% CV biomass in broiler diets is effective in influencing immune responses related to inflammatory status and promoting broiler growth.