Using alkali-metal cation-substituted zeolites and 2,4,6-trihydroxyacetophenone (THAP), which is a typical organic matrix molecule for matrix-assisted laser desorption ionization (MALDI), mass spectrometry has been performed for maltohexaose and acetylsalicylic acid, and the cation-selective ionization of these analytes was achieved. It is found that a complex of cation-substituted zeolite and THAP can be applicable to a compound that is hard to be ionized by a proton adduction in conventional MALDI.