The work presents analysis results of trends in the average seasonal air humidity within the atmospheric boundary layer of Siberia over 1981–2020, estimated from the observation data of 24 aerological stations for winter, spring, summer, and fall. It has been established that the summer season makes the greatest contribution to the increase in the average annual air humidity in the atmospheric boundary layer of the region, especially near the earth's surface, and to a lesser extent − spring and fall. Changes in the average seasonal air humidity for 1981–2020 were compared with the previously studied period 1981–2010.