The paper deals with the determination of the number of sapwood annual rings in oak ( Quercus sp.) in relation to altitude, locality and stand age. Several different groups of samples were used from two localities of south- ern Moravia. The results of the study demonstrate the effects of site water regime and age on the growth of sapwood annual rings. On the other hand, the effect of altitude was not proved. The information can be of crucial importance for the dendrochronological dating of an incomplete sample for particular regions where sapwood is partly or totally missing.