OBJECTIVE We studied the colonization ability and the distribution of the recombinant Lactobacillus casei in mouse intestine. METHODS We used Green fluorescent protein (GFP) gene as reporter in constructing the recombinant plasmid pLA-GFP,which was electrotransformed into the host cells L. casei. Six-week-old female SPF BALB/c mice were orally fed with the recombinant L. casei of approximately 10(9). Groups of at least three mice per condition were killed at 1. 5 h, 3 h, 12 h, 1 d, 3 d, 5 d, 6 d, 7 d,and its duodenum, jejunum, ileum, caecum intestinal tract rinse solution was sampled separately. The recombinant bacteriain intestinal tracts were examined by plate culture count. RESULTS The molecular weight of the recombinant protein was about 69 kDa in the result of western blot. The GFP fusion protein on the cell surface was confirmed by fluorescence microscopy and flow cytometric analysis. A portion of the recombinant L. casei was able to adhere and colonize in different regions of murine intestinal tract, and the planting peak was appeared on day 6 postinoculation. The ratio of the seventh day to the first day of the recombinant L. casei adhered to the intestinal mucosa in the duodenum,jejunum, ileum, and caecum was 16.49%, 25.08%, 47.71%, and 41.03%, respectively. CONCLUSION The recombinant L. casei stably expressing GFP could colonize mouse intestine. The field planting rule was ileum > caecum > jejunum > duodenum. Our findings indicated that L. casei used as a deliver vector in oral vaccine is feasible, but the impact on intestinal immune mechanism in mice is needed more research.