The present study was conducted to investigate in vitro and in vivo antibacterial activity of the root bark extracts of Anogeissus leiocarpa (DC) Guill. & Perr, in Escherichia coli extended-spectrum βlactamases (ESBL)-induced diarrhea in rat. The antibacterial activity was performed in vitro by determining the inhibition zone using standard agar diffusion method as well as in vivo on E. coli infected Wistar rat model. Both minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were carried through microdilution method. Results obtained in this study indicated that ethanolic and acetatic extracts were only active on bacteria presenting an inhibition zone range from 8 to 16 mm. The MIC observed in agar slant tubes ranged from 6.25 to 50 mg/ml. The ethanolic fraction of A. leiocarpa (ETHA) showed the highest in vitro antibacterial activity against strains with MICs ranging from 6.25 to 12.5 mg/ml and MBCs ranging from 12.5 to 25 mg/ml. In vivo, after infection, diarrhea increased faeces frequency, weight and volume faeces and bacterial faeces load to a maximum on the 2nd day after infection (P < 0.01). ETHA normalized the appearance, weight, volume and water content of faeces. To all doses, like ciprofloxacin it reduced significantly (P < 0.05) the bacterial growth compared to control Lot (infected and untreated). The death rate in diarrheic control Lot was 50% by Day 14. No death was recorded in Lot treated with ciprofloxacin and Lot treated with ethanolic fraction at dose of 2222.22 mg/kg body weight (bw). This study supports the use of A. leiocarpa in the traditional treatment of bacterial infections and offer many perspectives in the search for new molecules against resistant microbial strains.