HilA is a central regulator of Salmonella pathogenicity island 1 (SPI1), which is necessary for host invasion by Salmonella and induction of gastroenteritis. The iagB lies downstream of hilA and is thought to be co-transcribed with hilA, but iagB expression has not yet been analyzed directly. In this study, iagB expression in various mutant strains was measured to determine whether the expression pattern was similar to that of hilA. A β-galactosidase assay revealed that iagB expression was greater under shaking than standing culture condition. iagB expression was decreased in relA/spoT and ihfB mutants but not in luxS mutant, in line with previous reports on hilA expression. The hilA and iagB mRNA levels decreased by approximately 2-fold in arcA mutant grown aerobically and increased by approximately 10-fold in fnr mutant grown anaerobically. Although the fold changes in hilA and iagB mRNA level differed in hfq mutant strain, the patterns of time- and Hfq-dependent regulation were similar for both genes. Thus, iagB and hilA exhibited similar expression patterns in various mutational backgrounds and under different growth condition.