The need for cleaner environment concerns motivates the development of more efficient catalytic system. Based on this consideration, recently a novel catalyst named "Phase-boundary catalyst", a bimodal amphiphilic solid catalyst, was proposed. It was demonstrated that the catalytic system containing phase-boundary catalyst required neither stirring to make an emulsion nor addition of a co-solvent to make a homogeneous solution to drive the reaction. The driving force that has prompted this paper is to investigate the surface structure of alkylsilylated HZSM-5 as phase-boundary catalyst. Temperature Programmed Desorption (TPD) of ammonia and, 13C and 29Si MAS NMR spectroscopy were used to elucidate the surface structure of alkylsilylated HZSM-5. It is suggested the addition of small amount of water to the solid particles before alkylsilylation, as a recipe to make a bimodal amphiphilic particles, is desired to enhance the acidity of HZSM-5. The enhancement of acidity might be induced by polymeric octadecylsiloxane as elucidated by 13C and 29Si MAS NMR spectroscopy