Abstract: OBJECTIVE To establish a rat model of slow transit constipation by using loperamide, and to observe the transmission of colonic transit particle in this model. METHODS Thirty healthy SD rats were randomly divided into experimental group and control group. In the experimental group, loperamide was injected intraperitoneally for 21 d, and the control group was given the same amount of sterile water for injection. Body weight, the number of 24 h defecation, wet weight, dry weight, water content of faeces, and intestinal transit time were compared among two groups. At the end of the modeling, the colonic transit particles were infused into the rats, then observe its transmission in rats through performing the abdominal X-ray of rats at different times. RESULTS There was no significant difference in the food intake and drinking water between two groups. At the end of modeling, there was no significant difference in body weight between two groups. The number of 24 h defecation in experimental group was significantly lower than that in the control group (P<0.01), and the difference in the wet weight (P<0.01), the dry weight (P<0.05) and water content(P<0.01) of faeces in experimental group were significantly lower than those in control group. The gastrointestinal transit time of the experimental group was significantly longer than that of the control group(P<0.05). The rate of discharge of colonic transit particles in experimental group in 6 h and 12 h was significantly smaller than that in control group (P<0.05). CONCLUSION The model of rat constipation is established successfully. It was proved that the colonic transit particle is beneficial to diagnose slow transit constipation in rats.