As far as the most winterers in Antarctic expeditions mentioned sleep problems its monitoring and early disturbances evaluation may be of very importance for the entire mission. There are a lot of factors disturbing sleep, but such a challenging combination that embrace the effects of fluctuations in meteorological and climatological conditions, physical inactivity, social isolation, sensory and sexual deprivation is difficult anywhere to find. Each of the factors mentioned, even separately, can influence sleep. The decline in sleep quality and quantity, in turn, may affect the performance and adaptability of the crew members. The aim of the study was to investigate the changes in sleep in winterers of 21st Ukrainian Antarctic expedition during 2016-2017 years season at the “Akademik Vernadsky” Research Base. Twelve winterers (from 22 to 63 years old, all men) participated in subjective sleep quality measures study (IDS-SR30 questionnaire first four questions were analyzed). Four of them were involved in the objective sleep measurements. Personal smartphones with installed Sleep as Android app (Urbandroid Team) were used for sleep registrations. Based on built-in accelerometer data the total sleep time (TST) and deep sleep time (DST) were calculated by the program. The differences between subjective normal and actual daily TST were defined as increments or decrements in TST. The data for the last month of stay in Antarctica (March) and data for one or two months (at winterers C and D, problems with registration) were excluded from the analysis. Data were means±SD, compared by ANOVA. Despite personal variations in subjective reports in winterers, the sum of IDS-SR30 marks increased in winter-spring time which indicates a decrease in subjective assessments of sleep quality. All 4 subjects had individual peculiarities of sleep pattern and both in TST and DST changes during the year as well. Average yearly TST were 5.96±0.5 (n=11), 6.52±0.63 (n=11), 7.73±0.85 (n=9) and 7.78±0.4 (n=10) hours in A, B, C and D winterers correspondingly. TST duration over the year decreased in A and B, but increased in C and D winterers (Table). Thus, subjective reported sleep quality slightly declined, as well as two opposite strategies in TST changes in winterers were found in the research.