Th is paper concentrates on the Early Oligocene palaeoclimate of the southern part of Eastern and Central Europe and gives a detailed climatological analysis, combined with leaf-morphological studies and modelling of the palaeoatmospheric CO 2 level using stomatal and δ 13 C data. Climate data are calculated using the Coexistence Approach for Kiscellian fl oras of the Palaeogene Basin (Hungary and Slovenia) and coeval assemblages from Central and Southeastern Europe. Potential microclimatic or habitat variations are considered using morphometric analysis of fossil leaves from Hungarian, Slovenian and Italian fl oras. Reconstruction of CO 2 is performed by applying a recently introduced mechanistic model. Results of climate analysis indicate distinct latitudinal and longitudinal climate patterns for various variables which agree well with reconstructed palaeogeography and vegetation. Calculated climate variables in general suggest a warm and frost-free climate with low seasonal variation of temperature. A diff erence in temperature parameters is recorded between localities from Central and Southeastern Europe, manifested mainly in the mean temperature of the coldest month. Results of morphometric analysis suggest microclimatic or habitat diff erence among studied fl oras. Extending the scarce information available on atmospheric CO 2 levels during the Oligocene, we provide data for a well-defi ned time-interval. Reconstructed atmospheric CO 2 levels agree well with threshold values for Antarctic ice sheet growth suggested by recent modelling studies. Th e successful application of the mechanistic model for the reconstruction of atmospheric CO 2 levels raises new possibitities for future climate inference from macro-fl ora studies.