The study evaluated the immunological effect of extract of Momordica cochinchinensis (Lour.) Spreng. seeds (ECMS) on the immune response against Newcastle disease (ND) in chickens. Forty-eight chickens were divided into 4 groups (n = 12). Each chicken was immunized with ND vaccine mixed with 0, 20, 40, or 80 microg of ECMS on d 35. Blood samples were collected on d 0, 7, 14, 21, 28, and 35 postimmunization. Humoral and cellular immune responses were evaluated by indirect ELISA assay and the 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide method. Results indicated that humoral immune response was enhanced by ECMS 14 d postimmunization. Eighty micrograms of ECMS was the best dose with the ND vaccine and was significantly different from the other groups 21 d after immunization. No significant differences were found in the cellular immune response, whereas the 80 microg of ECMS group had higher values than the other groups 35 d after immunization. No side effect was found on the growth performance during the experiment.