In this work, four residual biomasses from the food industry (coconut husk, defatted grape seeds, sugar cane bagasse, and pressed palm fiber) were subjected to subcritical water hydrolysis assisted by CO2 (SubWH + CO2) with the objective of producing fermentable sugars. Hydrolysis kinetics were determined using a semi-batch unit equipped with a 50 mL reactor. The process was conducted at 250 degrees C for 30 min under 20 MPa. Total reducing sugars recovered using SubWH + CO2 were (wet basis): 13.5% for coconut husk, 10% for defatted grape seeds, 13.2% for sugar cane bagasse, and 11.2% for pressed palm fiber. For coconut husk and defatted grape seeds, adding CO2 increased total reducing sugars by 15 and 56%, respectively. For sugar cane bagasse and pressed palm fiber, adding CO2 to the process did not alter total reducing sugars recovered. In all cases, the byproduct yield increased when adding CO2 to the process.