Objective  To study the nervous mechanism underlying gastrointestinal dysmotility by observing the change of nitric oxide synthase(NOS) neurons in colonic myenteric plexus of the enteric nervous system (ENS）in rats with severe acute pancreatitis (SAP)complicated by gastrointestinal dysmotility.   Methods  Twenty Sprague Dawley rats were randomly divided into sham operation group and SAP group. A SAP model was induced by retrograde cholangiopancreatography-guided injection of 5% sodium taurocholate. Abdominal X-ray findings and small intestinal impelling ratio were detected. Pancreatic lesion was scored. Whole mount samples of myenteric plexus were prepared and stained with double immunofluorescence to observe the morphology of NOS neurons. The percentage of NOS neurons in the total neurons was calculated.   Results  The intestine was much more expanded

the small intestinal impelling ratio was significantly lower （P0.01）

the score of pancreatic lesion was remarkably higher （P0.01）

the NOS neurons were bigger and more deeply stained

and the nerve fibers between ganglions of the NOS were thicker in SAP group than in sham operation group. The percentage of NOS neurons was (40.74±5.15)% in SAP group

which was significantly higher than that in sham operation group （P0.01）.   Conclusion  A high expression level of NOS neurons in colonic myenteric plexus may be one of the nervous mechanisms underlying gastrointestinal dysmotility in SAP rats.