Wall-coated HZSM-5 with micro- and nanoscale crystal sizes were prepared and coated to the inner surface of SS304 stainless-steel tubes using washcoating methods. It was found that nanoscale HZSM-5 zeolite slurry has different rheological properties, washcoat loadings, and adhesions with microscale HZSM-5. Catalytic activities of the prepared micro- and nanoscale HZSM-5 zeolite coatings were studied using catalytic cracking of supercritical phase n-dodecane (550 degrees C and 4 MPa), indicating that catalytic cracking activity and stability were remarkably improved more than 1 time by nanoscale HZSM-5, coatings compared to microscale HZSM-5 coatings. Acid and pore structure characterization showed that the better performance of nanoscale HZSM-5 coating may be attributed to the shorter diffusion length of the micropore, the higher diffusion rate of supercritical n-dodecane in the intracrystal mesopore, and the special acid nature of nanoscale HZSM-5 coatings.