The analysis has revealed quasi-periodic long-term fluctuations of an annual flow for the majority of the rivers of Belarus. Statistically authentic correlation between a flow of adjacent years for researched reservoirs practically is absent. Researches on presence of a trend have revealed one increasing and one decreasing trend. Results of the analysis of statistical uniformity testify that long-term fluctuations of a flow of water of the rivers of Belarus have homogeneous character except for some reservoirs for each of the used criteria.