Experiments were made to compare the effect of particle size of sulfonamide on the initial dissolution behaviour in sodium lauryl sulfate solution and in distilled water and the following results were obtained. 1) At agitation speed of 700 rpm, there was no difference of particle size on the initial dissolution in 0.1% and in distilled water but in 1% solution somewhat, and the difference appeared at agitation speed of 300 rpm with decrease in particle size. Results obtained in sodium lauryl sulfate solution showed a similar tendency while the instantly dissolving part increased with decrease in particle size, and this part dissolved instantly at first and the constant rate of dissolution followed in distilled water. 2) Plots of log dissolution rate constants vs. log agitation speed became linear with the same slope irrespective of particle size, when 0.1% and 1% solutions were used. Rank order for the dissolution rates of different particle size of powders was possible even at a relatively low agitation speed of 200 rpm.