AIM: To investigate gastrointestinal migrating myoelectric complex (MMC) and the effects of porcine motilin and ursodeoxycholic acid (UDCA) on MMC of gastrointestinaltract of different origins in fasted rats. METHODS: Three bipolar silver electrodes were chronically implanted on the antrum, duodenum and jejunum. Seven days later 24 experimental rats were divided into 2 groups.One group was injected with porcine motilin via sublingual vein at a dose of 20 μg/kg, the other group was perfused into stomach with UDCA. The gastrointestinal myoelectric activity was recorded 1 h before and 2 h after the test substance infusions into the rats.RESULTS: In all fasted rats a typical patt of MMC was observed. Among the totally 68 activity fronts recorded in fasted rats under control, 67% started in duodenum, and 33% in antrum. MMC cycle duration and duration of phase Ⅲ of antral origin were longer than those of duodenal origin. Administration of 20 μg/kg porcine motilin induced a premature antral phase Ⅲ of antral origin. But perfusion into stomach with UDCA resulted in shorter MMC cycle duration, longer duration of phase Ⅲ of duodenal origin,which were followed with shorter cycle duration and duration of antral phase Ⅲ.CONCLUSION: In fasted rats, MMC could originate from antrum and duodenum respectively. The characteristics of MMC of different origins may contribute to the large variations within subjects. The mechanisms of different origins of phase Ⅲ may be different. Porcine motilin and UDCA could affect MMC of different origins of the gastrointestinal tract in fasted state, respectively.