The work presents analysis results of trends in the average annual air humidity in the atmospheric boundary layer of Siberia for 1981−2020 according to observations of 24 aerological stations. It has been established that, in contrast to the average air temperature, which is characterized by positive trends throughout the entire atmospheric boundary layer of Siberia, negative trends in the average annual air humidity are observed from a height of 400 m in the south-west of the territory, and they prevail at 1600 m in Western Siberia to the west 7580 E and, partially, in the subpolar and temperate latitudes of Eastern Siberia. Changes in the average annual air humidity for 19812020 were compared with the previously studied period 19812010. The moisture content in the atmospheric boundary layer over Siberia increased almost throughout the region, with the exception of the central areas of Eastern Siberia, where a slowdown in the growth of air humidity is observed.