The effect of diluents on the dissolution rate of indomethacin was studied and the dissolution rate for the marketed products was compared to establish the quality standard for indomethacin preparation. The results are as fellows 1. The effect of test methods was not significant in the case of paddle method but was greatly effected in the case of basket method. 2. The effect of diluents was not significant generally, but in the case of starch dissolution rate was greatly effected. 3. The dissolution rate was remarkably decreased in proprotion to increase of capsule size. 4. The marketed products met the KP dissolution requirement but showed a little difference due to manufacturers.