Chitosan is a biopolymer with many potential applications in diverse industries, but the lack of information on its solubility and dissolution kinetics in green solvents limits the development of processes for producing high-added-value products. A medium-molecular-weight chitosan was characterized by size exclusion chromatography, viscometry, 1H NMR and UV spectrometry, and its solubilities in aqueous acetic acid and in pressurized CO2-water were determined using a high-pressure view cell coupled to a UV spectrophotometer. The solubility of chitosan in aqueous acetic acid was determined at 25, 30 and 50 °C, and in pressurized CO2-water from 7.4 to 66.4 bar at 25 °C and from 7.4 to 138.2 bar at 50 °C. The effect of temperature, solvent/chitosan molar ratio (or pressure for the CO2-water system), and average particle size on the solubilization time of chitosan in these solvents was determined. Short (19 to 35 min) solubilization times of chitosan in both solvents were observed.