Abstract: The aim of the study was to evaluate the adjuvant effect of Ginseng Stem-Leaf Saponins (GSLS) on the immune responses against Newcastle Disease (ND) in chickens. Birds were immunized (i.m.) with ND oil emulsion vaccines containing GSLS (0, 2, 4, 6 and 8 μg/0.2 mL). Blood samples were collected on Weeks 0-3 after immunization for the measurement of Hemagglutination Inhibition (HI) titers and splenocytes were prepared for Lymphocyte Proliferation test. The results showed that serum HI titers were significantly higher in group containing GSLS (2, 4 and 6 μg/0.2 mL) than in control group at Weeks 2 and 3 post immunization (p<0.05). Splenocyte stimulation indexes were significantly enhanced in chickens immunized with ND oil emulsion vaccine containing GSLS (6 μg/0.2 mL) when compared with control group at Week 3 post immunization (p<0.05). No abnormal behaviors and side effects were found in chickens between groups throughout the whole experiment. This suggests that GSLS and oil adjuvant can synergistically promote both humoral and cellular immune responses. Therefore, GSLS could be a promising vaccine additive to improve vaccines against infections in poultry.