The aim of the study was to examine the spatial autocorrelation and the optimal spatial resolution of optical remote sensing images in a forested landscape. Also the effect of tree species and forest age on this optimum was investigated. Two different methodologies were applied. Semivariograms were used to measure the autocorrelation of pixels while local variance curves were used to define the spatial resolution that maximizes the variance between neighbouring pixels. The range of the semivariograms was 5 m. for Scots pine and 7 m for Norway spruce. Range is also weakly dependent on forest age class. Thereafter sill was found to be strongly dependent on tree species and forest age class. The local variance maximum in infrared and green band was obtained with a spatial resolution of 3 m and in red channel with a resolution of 2 m. Like the semivariance the local variance was at a higher level in spruce and old forests.