Phenological observations of birch were conducted in the central part of Lithuania (Kaunas distr.), in pure 15–50-year-old B. pendula and B. pubescens stands in 2004–2006. Basically, phenological stages of foliation and flowering were studied. Heterogeneity and stability of the phenology of silver birch (B. pendula Roth.) and downy birch (B. pubescens Ehrh.) were investigated, phenological groups of flowering and foliation were identified, correlation of the development phases of vegetative and generative organs was analysed.