Antibody-toxin conjugates, termed immunotoxins, are currently being evaluated as potential new anticancer agents and one of the most extensively studied toxins for construction of immunotoxin is ricin which exists in the seeds of castor bean, Ricinus communis. Another toxic lectin from castor bean is RCA (Ricinus communis agglutinin). Both toxins are very homologous. We reported the puriffcation procedure and biological properties of ricin from the Korean castor bean in another place and here we report those of RCA. The purified RCA shows three bands on denatured SDS PAGE while ricin shows two bands. On cultured $K_{562}$ cells ricin and RCA both inhibit the multiplication of cells extensively. $30{mu}g/ml$ of ricin shows 73% of inhibition rate at day 4 compared to 68% in same condition of RCA. The inhibition of multiplication of cells are directly proportional to the concentration of toxins and the incubation period. In every case ricin was more toxic than RCA. The $LD_{50}$ dose of ricin on ICR mice was 60 ng at day 3 but that of RCA was $10{mu}g$.