Controlling the size of SBA-15 can be beneficial for exploiting CMK-3, which has excellent structural parameters, for better performance in adsorption and/or catalytic processes. In this study, the width of freestanding SBA-15 rods was readily and successfully regulated by simply altering the stirring power during the synthesis. A higher stirring rate produced SBA-15 rods with larger width. Then, the size of the CMK-3 rods was adjusted by duplication of the different-sized SBA-15. The results show that the larger sized CMK-3 has higher specific surface area and pore volume, which led to a higher adsorption capacity and a faster adsorption rate. It is believed that the synthetic method reported here is powerful for developing better mesoporous carbon for application in water purification and catalysis.