From this experiment we found that acetylcholine (Ach) was the agonist of the colonic smooth muscles, and noradrenaline (NA) the internal anal sphincter(IAS). The contractions of colonic smooth muscles were significantly inhibited under the calcium-free solution (Ｐ＜0.01), but the IAS was not affected. Ryanodine, which can exhaust the intracellular calcium, remarkably depressed the contractions of IAS (Ｐ＜0.01),but had no effect on the colonic smooth muscles. It can be concluded that the contractions of colonic smooth muscles are mainly related to the influx of extracellular calcium; the release of intracellular calcium plays an important role in the contractions of IAS.