A recombinant DNA, pMG36e::$luc^+$ (5.3 kb), was constructed and transferred to Escherichia coli MC1061 and Lactococcus lactis MG1363 for in vivo imaging of the bacteria in murine intestines. E. coli MC1061 (pMG36e::$luc^+$) and L. lactis MG1363 (pMG36e::$luc^+$) displayed luciferase activities in vitro, where the bioluminescent signal of the E. coli was much stronger than that of the L. lactis by approximately 100-fold. These 2 recombinant bacteria were orally administered into rats. The bioluminescent signals of the E. coli and L. lactis in the gastrointestinal (GI) tracts of rats were detected and maintained up to 2 h via whole body imaging, indicating that the luciferase gene expression system for bacteria could be applied for in vivo imaging.