BACKGROUND: This study is aimed at evaluating immunogenicity by measuring immunoglobulin A (IgA) seroconversion rate through common mucosal immune system and adverse reactions after vaccination of oral live attenuated Salmonella typhi (S. typhi) Ty21a vaccine in Korean population. METHODS: A commercially available oral live attenuated vaccine of S. typhi strain Ty21a (Zerotyph(r) capsule, Boryung Biopharma Co., Seoul, Korea) was given to volunteers; children above 6 years, adolescents, and adults who have never infected with S. typhi nor received S. typhi vaccination. The vaccines were given in three doses, with two day interval between the doses. Seroconversion was determined by ELISPOT (enzyme-linked immunospot) assay. Adverse reactions after vaccination were evaluated in 12 institutions by direct interviewing with vaccinees. RESULTS: A total of 93 volunteers for evaluation of seroconversion were enrolled. Seroconversion rate in the the below 16 year-old group was 73.8% (31/42) and that of over 16 year-old group was 86.3% (44/51), which was not statistically different. Adverse reaction were found in 8.6% (40/465). Gastrointestinal symptoms were most common (6.5%, 30/465). Adverse reactions were found in 5.2% (24/465) after 1st administration, 4.5% (21/462) after 2nd, and 2.6% (12/461) after 3rd. Frequency of adverse reactions was significantly higher after 1st administration (P<0.05). CONCLUSION: Oral live attenuated S. typhi vaccine, Zerotyph(r) capsule, had good immnuogenicity and safety through intestinal immune system.