Synthesis of Sn-Beta zeolites was studied by using a steam-assisted conversion (SAC) method. The effects of the amount of water in the bottom of autoclave, the crystallization time, the crystallization temperature and the gel drying temperature on the formation of the Sn-Beta zeolite frameworks, which have not been addressed before, were investigated in detail. An improved SAC autoclave was used for investigating the role of water in the formation of Sn-Beta zeolites. The characterization results of XRD, SEM, FT-IR, and UV-Vis for the as-synthesized samples show that the SAC method can rapidly produce pure and highly crystalline Sn-Beta zeolites. For the first time, we found that the interior construction of the conventional SAC autoclave can affect the formation of Sn-Beta zeolites. In the synthesis process, the condensed water over the gel changed synthesis composition. This issue was solved successfully by our improved autoclave. The optimized synthesis conditions of high quality Sn-Beta zeolites are the gel drying temperature of 333-373 K and the crystallization temperature of 433-473 K. (C) 2013 Elsevier B.V. All rights reserved.