Аннотация:The problem of the mixing layer height (MLH) determination with the use of the sodar data is discussed. Unlike the most of other methods a new suggestion is to determine separately two different mixing layer heights: “upper” or “stable” MLH which indicates a top of an inversion inside wind shear layer (in which dynamical turbulence exists and creates echo-signal) and “lower” or “unstable” MLH which indicates as a rule unstable or weak-stable stratification below the elevated inversion bottom. Some experimental data confirm that two different MLH sometimes, usually in the morning, exist simultaneously one above another. According to this idea the diurnal courses of mixing layer heights – both “upper”, and “lower” – have been calculated on a base of long-term sodar sounding at Moscow State University (MSU) during 15 years. Dynamics of both heights at various seasons is discussed.