High-surface-area aluminum hydroxide methoxide (CH 4 Al 2 O 4 ) nano- and microparticles are synthesized continuously in supercritical methanol (scMeOH). The properties of the particle synthesized in scMeOH are compared with those synthesized in supercritical water (scH 2 O). The XRD analysis reveals that the particles synthesized in scMeOH retain aluminum hydroxide methoxide crystalline structure while the particles synthesized in supercritical water retain boehmite (AlOOH) crystalline structure. Plate-shape particles are synthesized in scH 2 O while highly porous, flake-like particles are synthesized in scMeOH. Due to the porous structure, the CH 4 Al 2 O 4 particles have much higher BET surface area (314m 2 /g) than that of the boehmite particles (35.9m 2 /g). The FT-IR analysis indicates that aliphatic, carbonyl, and hydroxyl groups are present on the surface of the CH 4 Al 2 O 4 particles. When heat treated at 800°C, the CH 4 Al 2 O 4 phase is converted to γ-Al 2 O 3 phase with a BET surface area of 164m 2 /g.