Disclosed are a MWW/DDR type gas separation membrane comprising at least one MWW type zeolite and at least one DDR type zeolite and a method for preparing the same. One of the MWW type zeolite and the DDR type zeolite is disposed on the other thereof, wherein at least one of the MWW type zeolite and the DDR type zeolite is epitaxially grown. In the gas separation membrane, the DDR type zeolite is epitaxially grown from the MWW type zeolite, or the MWW type zeolite is epitaxially grown from the DDR type zeolite. Thus, the MWW/DDR type gas separation membrane is synthesized using a structural continuity of the MWW type zeolite and the DDR type zeolite. Thus, the gas separation membrane has excellent separation efficiency.