We present a study of peculiarities of the winter nighttime maximum in the critical frequencies f0F2 at mid-latitudes of the Asian region. The data of stations located at different longitudes and close latitudes have been used in the analysis: Novosibirsk (54.8°N, 83.2°E), Irkutsk (52.5°N, 104.0°E), and Khabarovsk (48.5°N, 135.1°E). It has been found that the nighttime maximum in f₀F2 is observed after midnight (02000400 LT) and is a stable feature of the quiet ionosphere from the middle of October to the middle of March at low solar activity (SA) at all analyzed stations. This interval decreases with increasing SA. The difference between the maximal and minimal f₀F2 values in nighttime hours is the largest in DecemberJanuary, and its amplitude is almost independent of SA. Variations in the critical frequency of the h_mF2 layer are inversely related to those in the height of the maximum. We have studied periods when the difference between the daytime and nighttime values of f₀F2 is less than 2 MHz. The intervals of observations of such events at different longitudes do not coincide. No dependence of the winter nighttime maximum amplitude on magnetic activity has been found.