Previous studies have demonstrated that phagocytosis of encapsulated bacteria needs the opsonization of bacteria with immunoglobulin and complement. Several investigators have studied the role of specific antibody to the bacteria. The purpose of this study is to investigate the role of specific anti-Actinobacillus actinomycetemcomitans Y4($A{alpha}Y4$) antibody, which was obtained from the immunized rabbit serum for phagocytosis of $A{alpha}Y4$ by PMNL. For this study, specific and nonspecific IgG were separated from the sera of the rabbits and PMNL were isolated from 15 healthy adults. By an enzyme-linked immunosorbent assay, the results showed that the binding capacity of anti-$A{alpha}Y4$ IgG to $A{alpha}Y4$ was much higher than that of nonspecific IgG; 0.75 and 0.14(O.D. at 400nm), respectively. The oxygen consumption of PMNL, phagocytizing $A{alpha}Y4$ which was opsonized with specific $A{alpha}Y4$ IgG(37.13 nmol/min/$1{ imes}10^7$ PMNL), was significantly higher than that with nonspecific IgG(27.95 nmol/min/$1{ imes}10^7$ PMNL, p<0.01). In immunofluorescence microscopic examination, the difference between the numbers of the ingested $A{alpha}Y4$ opsonized with specific anti-$A{alpha}Y4$ IgG and nonspecific IgG reached to statistically significant level; $184{pm}11.4$ and $133.2{pm}8.3$ per 100 PMNL, p<0.05. These results suggest that specific anti-$A{alpha}Y4$ IgG has a significant role in PMNL phagocytosis of encapsulated $A{alpha}Y4$ and also it can be available to adopt this system to develop anti-capsular antibody to $A{alpha}Y4$ for enhancing and emphasizing the phagocytic activity against this bacterium.