The present study, conducted during the period 2010- 2011, involved morphological observations and anatomical investigations of horse chestnut (<i>Aesculus hippocastanum</i> L.) leaves with symptoms of damage caused by feeding of larvae of the horse-chestnut leaf miner (<i>Cameraria ohridella</i> Deschka & Dimić). Leaves were collected from trees growing in the city of Lublin (Poland). Microscopic slides were prepared from fresh and fixed plant material. Leaf anatomical features were examined by light microscopy in order to determine the mechanical barrier for feeding pests. Changes were also observed during the progressive damage of the leaf tissues caused by the larvae. Selected developmental stages of the pest are presented in the paper. It has been shown that very thin blades of the mesomorphic leaves of <i>Aesculus hippocastanum</i> produce a poorly developed mechanical barrier in which the following elements can be included: the presence of collenchyma and idioblasts with druses of calcium oxalate, few non-glandular trichomes found close to the leaf veins as well as relatively thin outer walls of the epidermal cells. The cells containing tannins and the oil cells found in the mesophyll may form a physiological barrier. However, foraging leaf miner larvae feed only on the palisade and spongy parenchyma cells, leaving undamaged the cells with tannins as well as the idioblasts with calcium oxalate crystals and oils. The feeding of the pest in the leaf mesophyll leads to the death of the epidermis on both sides of the lamina and to drying of the parts of the leaves in the area of the mines.