Particle size analysis of synthesized Al2O3 by dissolution and alkali fusion-coprecipitation methods has been conducted. The formation of nano-or microparticles can be synthesized by the top-down (physically) and bottom-up (chemically) methods. In this study, the commercial alumina (Merck) with the particle size of 63 µm was synthesized through the bottom-up method. The dissolution method was done by reacting to alumina with ammonium hydroxide (NH4OH). The alkali fusion method was carried out by reacting alumina with sodium hydroxide (NaOH) and it obtained by coprecipitation of the alkali fusion product with HCl and NH4OH. The result from both methods were calcined at 600°C. The phase of synthesized Al2O3 was identified by using X-ray diffraction (XRD), whereas the morphology observed using a transmission electron microscope (TEM), and the particle sizes measured by particle sizes analyzer (PSA). The XRD pattern shows the γ-Al2O3 phases with particle sizes of ~33 nm and ~25 nm from TEM observations, while the PSA results revealed agglomerated particles with particle sizes of 1263 nm and 477 nm for the dissolution and alkali fusion-coprecipitation method, respectively. Therefore, both methods can be used to reduce the particle size of γ-Al2O3.