Dried whole plant parts of Ludwigia hyssopifolia were subjected to successive cold extraction with n-hexane, ethylacetate and methanol. The methanol extract (LHM), obtained as 1% yield, showed significant antidiarrheal property by reducing diarrheal episodes in castor oil and serotonin induced diarrhea in laboratory mice at a dose of higher than 100 mg/kg body weight as compared to standard drug loperamide given at a dose of 66.67 microg/kg body weight. The percent reduction in diarrheal episode by 56.32 and 89.66 after castor oil challenge and 59.09 and 86.36 in serotonin induced diarrhea was observed at doses of 200 mg/kg and 400 mg/kg body weight of the extract respectively. The extract LHM was also found to reduce the gastrointestinal motility by 53.8% at a dose of 100 mg/kg body weight as compared to control, while no remarkable inhibition of gastrointestinal motility was seen at a dose of 50 mg/kg body weight of the extract.