Objective To investigate the drying methods and optimal time for internal suction biopsy channel dryness for flexible endoscope.Methods Flexible gastroscopes or colonoscopes after clinical use were randomized into 5 or 6 groups.After standard reprocessing steps, drying was performed either manually (forced high-efficiency particulate filtered air with a Safety Air Gun for 30 seconds) or was automated (endoscope drying device) for 5 minutes and then added manual drying for either 30,40,50,60 or 70 seconds(the 6th group of the colonoscope).The experiments repeated 60 times for each group.Drying effectiveness was measured using cobalt chloride paper after drying.Results The rate of dryness using manual drying was 20.0% for gastroscope and 18.3% for colonoscope.The rate of dryness for gastroscope achieved 100% at 60 s of manual drying on the basis of automated drying, or at 70 s for colonoscope.The dryness rates among different gastroscope groups and colonoscope groups had significant differences (both P＜0.05).Conclusion Using automated drying for 5 minutes, internal suction biopsy channel can achieve dryness by adding manual drying for either 60 seconds for the gastroscope or 70 seconds for the colonoscope.