In order to search the availability of the lectin extracted from Korean mistletoe(Viscum album coloratum) as an adjuvant for the avian vaccines, attempts were made to determine toxicity of the lectin in chicks and its immunostimulating activity on the inactivated vaccines against Newcastle disease virus(NDV). For the determination of toxicity, the lectin was injected into the thigh muscle of SPF chicks(Charles River) of 1-week-old and observed hematologically and pathologically. For the determination of immunostimulating effects, lectin-adjuvanted, inactivated NDV vaccines were injected into the thigh muscle of SPF chicks in the same age group. Sera of the chicks were examined for the hemagglutination-inhibition(HI) antibodies induced, their HI titers and reaction to the NDV antigens. The data were further compared with those from aluminum hydroxide [$Al(OH)_3$]-adjuvanted vaccines and vaccines without adjuvant, and the results are as follows. There were no significant changes observed in the values of RBC, WBC, Hb, PCV, MCV, MCH, MCHC, AST, ALT, BUN, creatinine and total proteins in the chicks administered with lectin of 1.1, 2.2 and $22.2{\mu}g/kg$ body weight, which means the lectin has no effects on blood values and functions of liver and kidney. In histopathologic observation, no lesions were observed in the brain, heart, liver, lung, spleen, kidney, thymus and bursa of Fabricius of the chicks administered with lectin of 1.1, 2.2 and $22.2{\mu}g/kg$ body weight. There were inflammatory lesions, such as congestion, hemorrhage, edema, infiltration of macrophages and coagulation necrosis observed in the thigh muscle of chicks administered with lectin of $22.2{\mu}g/kg$ body weight, whereas no changes were observed in 1.1 and $22.2{\mu}g/kg$ lectin administered chicks. In chicks immunized with lectin($4.4{\mu}g/kg$ of body weight)-adjuvanted B1, LaSota and Ulster 2C vaccines, HI titers in reciprocal values for $log_2$ were 1.8-2.2 at 1 week after vaccination, which was similar with those of 1.5-2.9 by $Al(OH)_3$-adjuvanted vaccines. The HI titers by the lectin-adjuvanted vaccines reached to 3.9-5.3 at 4 weeks, whereas those by the $Al(OH)_3$-adjuvanted vaccines were more high as 7.3-9.3. Meanwhile, the immunostimulating effects of the lectin were recognized while compared to the HI titers with 2.4-3.7 in chicks immunized with vaccines without adjuvants at 4 weeks after vaccination. The chicks immunized with lectin-adjuvanted vaccines were enough to resist challenges by Kyojeongwon strain, a very virulent NDV at 4 weeks after vaccination as well as chicks immunized with $Al(OH)_3$-adjuvanted vaccines. The HI titers by the lectin-adjuvanted vaccines reached to high level as 8.7-10.3 as those with 8.2-9.6 by the $Al(OH)_3$-adjuvanted vaccines at 6 weeks after vaccination, which may be the booster effects by the challenge virus. Antibodies specific to the HN and F antigens of NDV were observed in the sera of both chicks immunized with lectin-adjuvanted vaccines and $Al(OH)_3$-adjuvanted vaccines.