Several approaches have been tested to reduce the size of mesoporous tin oxide (m-SnO2) agglomerates prepared by utilizing the self-assembly of n-cetylpyridinium chloride. The variables and methods tested were the mixing ratio of Na2SnO3·3H2O as a tin source and trimethylbenzene in the precursor solution, stirring or ultrasonic treatment after the hydrolysis of the precursor solution, and mechanical grinding of resulting m-SnO2 powders in an agate motor. Among them, ultrasonic treatment immediately after the hydrolysis of Na2SnO3·3H2O was very effective in reducing agglomerate size and in obtaining a large specific surface area (SSA) of more than 300 m2 g−1, even after calcination at 600°C for 5 h, while grinding in the agate mortar after the calcination led to a decrease in SSA of all m-SnO2 powders. The m-SnO2 sensor fabricated with ultrasonically treated powder showed relatively high H2 sensing properties, probably owing to the small-size agglomerates and large SSA