Diarrhea is one of the common refractory symptoms in patients with depression. Probiotics are effective in alleviating common diarrhea， but the effect of probiotics on diarrhea in depressed patients remains unclear. In this study， the effect of Lactobacillus paracasei L9（L9） on diarrhea in rats with depression was investigated by using a rat model induced by chronic mild stress （CMS）. The results showed that， compared with the control group， CMS rats showed lower sucrose preference， more immobility in force swimming test and less activity in center zone of open field test. Meanwhile， the number of stool pallets， dry weight and water content of stool were increased， and the transit time of the whole gut was shortened in CMS rats. These results indicated CMS induced depressive-like behavior which accompanied by diarrhea-like symptoms in rats. L9 administration significantly decreased the number of stool pallets， dry weight， and water content of stool， and increased the whole gut transit time in depressed rats with diarrhea. Furthermore， it was found that the mRNA level of 5-HT4 receptors in the colon of depression and diarrhea rats was abnormally increased. After intervention by L9， the transcription level of 5-HT4 receptors was significantly reduced.