To evaluate the degree of competitive exclusion against Salmonella gallinarum(S. gallinarum) of Salmonella enteritidis(S. enteritidis) infected chickens, fifty-six, 4-week old Hyline layer suspected of S. enteritidis infection were challenged with S. gallinarum. All chickens were tested for S. enteritidis isolation using cloacal swabs and serum plate agglutination test using S. enteritidis Ag. before challenge and classified into four groups(SE isolated, SE nonisolated, SE seropositive and SE seronegative). None of the SE isolated and the SE seropositive groups died after challenge and the average weight gains were 245.5g and 254.6g, respectively. But in the SE nonisolated and the SE seronegative groups, mortality was 18.2% and 20.6% and the average weight gains were 150.1g and 111.2g. The incidence of reisolation of S. gallinarum of the SE isolated and the SE seropositive groups were 41.7% and 47.6% from liver, 33.3% and 47.6% from spleen and 8.3% and 14.3% from cecum, respectively, and the SE nonisolated and the SE seronegative group were 63.6% and 64.7% from liver, 84.1% and 88.2% from spleen and 47.7% and 52.9% from cecum. The serological response of the SE isolated and the SE seropositive groups hardly changed from 75.0 and 81.8% before challenge to 75.0 and 85.7% after. But, the other two groups were found to be significantly higher after challenge and increased from 0 and 18.2% to 100%. Consequently, S. enteritidis preinfected chickens were found to be significant different in terms of mortality, weight gain, reisolation of S. gallinarum and serological response compared to noninfected chickens. Moreover, our study shows that S. enteritidis infected chickens appear strong competitive exclusion against the colonization of S. gallinarum.