Comparative study on catalytic conversion of methanol and propanal over Ga/ZSM-5 is reported in this paper. A series of Ga/ZSM-5 catalysts were obtained by post modification of ZSM-5 in a mixture of Ga(NO3)(3) and NH4HF2. The obtained zeolite samples were subjected to detailed characterization and catalytic evaluation in methanol and propanal conversion reactions. It was found that the post-modification step by Ga(NO3)(3) and NH4HF2 had effects both on structure and acidity: (1) decreasing both acid concentration and strength as indicated by NH3-TPD, FT-IR analysis and elemental analysis, (2) selective removing the defective zone of ZSM-5 zeolite, and (3) depositing Ga species on zeolite. The catalyst lifetime in methanol conversion reaction was dramatically improved after post-modification; the longest catalyst lifetime of Ga/ZSM-5-1 observed was 14 days. On the contrast, the catalyst lifetime in propanal conversion was kept constantly at 8 h over all zeolite samples. The different effects of zeolite after post-modification in methanol and propanal conversion are due to the reactivity difference between methanol and propanal. (C) 2015 Elsevier Ltd. All rights reserved.