Abstract: Based on the two content distribution curves obtained by assaying domestic tablets which contain very small amounts of active ingredients, we have studied some of the statistical characteristics of the USP ⅩⅪ content uniformity sampling plan for tablets and compared them with those of the USP ⅩⅩ by means of computer simulation. Some quantitative results have been obtained, which showed that the decision accuracy of the USP ⅩⅪ content uniformity sampling plan is much better than that of the USP ⅩⅩ plan. Owing to the introduction of RSD the USP ⅩⅪ plan become a mixed, by-attribute and by-variable sampling plan, while the USP ⅩⅩ plan belongs to the realm of the pure by-attribute type.