High-surface-area aluminum hydroxide methoxide (CH₄Al₂O₄) 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 (scH₂O). 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 scH₂O while highly porous, flake-like particles are synthesized in scMeOH. Due to the porous structure, the CH₄Al₂O₄ particles have much higher BET surface area (314m²/g) than that of the boehmite particles (35.9m²/g). The FT-IR analysis indicates that aliphatic, carbonyl, and hydroxyl groups are present on the surface of the CH₄Al₂O₄ particles. When heat treated at 800°C, the CH₄Al₂O₄ phase is converted to γ-Al₂O₃ phase with a BET surface area of 164m²/g.