This study was conducted to test the efficacy of Ulva pertusa kjellman as immunomodulators under lipopolysaccharide(LPS) challenge in broilers by investigating their effects on serum superoxide dismutase(SOD) like ability, immunoglobulin concentration, and splenic cytokine mRNA expression. A total of ninety six1-d-old male broiler chicks(Ross 308) were divided into 4 treatment groups with 8 replicates of 3 birds in each group. NC(negative control, no immune substances), PC(positive control, β-glucan 25 ppm), Ulva P(Ulva pertusa kjellman Powder 3%), and Ulva E(Extract form Ulva pertusa kjellman 0.3%) were added in feed with respective substance. Heparinized venous blood and spleens were collected from five birds per dietary treatment at 5 wk of age. The SOD like activities in Ulva P and Ulva E were significantly increased in comparison with other groups(P<0.05). The immunoglobulin M content was lower in the Ulva E than other groups(P<0.05). Expression patterns of splenic cytokine mRNA in the IL-1β, IL-2 and IL-6 were similar. Expression rate of IL-1β, IL-2 and IL-6 in Ulva pertusa kjellman(Ulva P, Ulva E) were decreased(P<0.05) in comparison to other groups. Expression rate of IL-1β, IL-2 and IL-6 were significantly lower in groups treated with Ulva E than Ulva P. In conclusion, dietary supplementation of Ulva pertusa kjellman improved SOD like activity and affect immune system by inhibiting inflammatory response in broiler chicks. In addition, it is more effective to use Ulva pertusa kjellman extract than powder for immunomodulatory function. These results suggest the possibility that Ulva pertusa kjellman could be used as the immunomodulator for inflammatory response in broiler chicks.