The organosolv-fractionation process can act as a biorefinery process because it can separate the main components of biomass, such as lignin and hemicellulose, with high purity. The ethanol-based organosolv-fractionation process was applied to separate carbohydrates and lignin from rice husks, and the extraction behavior was observed according to various reaction variables. Various reaction conditions such as different temperatures (150 °C, 170 °C, and 190 °C), reaction times (30 min, 60 min, and 120 min), and ethanol concentrations (40%, 60%, and 80%) were tested while maintaining the solid:liquid ratio (1:10) and sulfuric acid concentration (0.25 wt.%). Two optimal reaction conditions for the target components were chosen: for sugar recovery, 150 °C, 60 min, and 40% ethanol were used as condition 1, and for lignin recovery, 170 °C, 120 min, and 80% ethanol were used as condition 2. Under condition 1, 91.5% of the glucan was preserved in the residual solid, and 75.0% of the xylan was extracted from the liquid hydrolysate. For condition 2, 59.9% of the lignin was recovered. To properly choose and apply the correct fractionation method and conditions, the reaction behavior (such as carbohydrate retention and extraction), lignin solubilization, and precipitation should be carefully considered.