The effect of particle on the catalytic activity of HZSM-5 zeolite in organosolv lignin to phenols was investigated in the supercritical ethanol-water under the operating conditions of 350 °C and 4 h. Two samples comprising a micro and a nano size HZSM-5 were prepared by reflux and hydrothermal crystallization method, respectively. The catalyst samples were characterized with XRD, SEM, BET and NH3-TPD analytical techniques. The effect of crystal size on the lignin conversion to phenols and the structure changes of lignin residue were studied. The nano-HZSM-5 showed higher yield of phenols and lower yield of char as compared to the micro-HZSM-5. The enhanced content of aromatic C-C structures and extenuative content of aromatic C-O and C-H showed that intramolecular dehydration and deoxygenation were occurred with nano- and micro-HZSM-5, and the nano-HZSM-5 activity significantly stronger than micro-HZSM-5.