Seasonal course of actual albedo (i.e. the ratio of upward to downward short wave radiation flux) generalized by polynomial approximation was compared with the course of idealized albedo (calculated supposing constant surface optical properties) and the course of leaf development in a floodplain forest (mostly oak) in southern Moravia. Rapid increase of actual albedo in spring was evidently caused by flushing of young leaves from the end of April to mid-June. The reflectance of leaves decreased with time which could be seen at a slight decrease of albedo up to mid-August, when leaves were definitely developed. The albedo increased rapidly again at the autumn up to the beginning of November. The comparison of actual and idealized seasonal courses of albedo enables to formulate following conclusions: The seasonal course of albedo at the first part of growing season can be used as an indicator of leaf development in a broadleaved forest. The increase of albedo in autumn can be explained by an increased specular reflection effect due to small sun elevation. Mean seasonal transmissivity and air mass number as regional atmosphere characteristics can also be estimated from the above mentioned data.