Hinokitiol has been widely used as a hair growth-promoting agent, as well as an anti-inflammatory compound incosmetics and pharmaceuticals. Because the particle size of a drug impacts its bioavailability, reducing the particle size ofa bio-active substance can improve its bioavailability. In this study, hinokitiol is micronized by the rapid expansion of asupercritical solution. Supercritical carbon dioxide was selected due to its relatively low critical temperature and pressure. Experiments were conducted in order to investigate the effects of temperature (313.15~333.15 K) and pressure (10.0~15.0MPa). Study results demonstrated that the isobaric increase in temperature lead to an increase in the average particle sizefrom 1.74 to 2.76 μm. Furthermore, the isothermal increase in pressure resulted in a decrease in the average particle sizefrom 2.21 to 1.14 μm. Additionally, the effects of temperature and pressure on particle size were assessed through anexamination of solubility data and thermodynamic behavior.