Ketene was made from acetic acid over MCM-41. Ketene could be separated with other byproducts by using low temperature trap, and reacted with acetic acid to form acetic anhydride. Acetic anhydride was not formed without catalyst and could be only formed via ketene intermediate over silica catalyst. Increases of the carrier flow rate caused the increase in activity and the optimum temperature was 823K. The activity of MCM-41 was much higher than that of amorphous silica which had no pore.