Horse chestnut (Aesculus hippocastanum L.) is a deciduous woody plant form family Hippocastanaceae. Due to its aesthetic and economic characteristics, it is grown as an ornamental tree in urban areas, city parks, streets and alleys as a solitaire or in groups, and in tree rows. Chestnut is not only an ornamental tree, but also an important bioindicator of polluted environment. The role of greenery in urban areas is multiple: aesthetic, social and ecological. Chestnut trees contribute to air purification, noise reduction, balance of gases in the air, modification of temperature extremes, thus contributing to mitigating climate change and increasing the green areas of cities. Horse chestnut hosts several harmful organisms. Its most important pest is the horse chestnut leaf miner moth (Cameraria ohridella Deschka et Dimić). The caterpillars of the chestnut miner moth feed on the parenchymal cells of the leafs mesophyll. Nutrition reduces the amount of photosynthetically active tissue, thus reducing the assimilation potential of the leaf itself. The aim of this research was to examine the extent to which the attack of the miner moth caterpillar affects the reduction of the assimilation potential of the horse chestnut leaf. For the purpose of research, three generations of pests were monitored. Attacked leaves were sampled in three periods. The first sampling was done at the beginning of May, the second at the beginning of June and the last at the end of June. For each sampling, 50 attacked leaves were collected. The leaves were then photographed on the same day. The photos were processed in the computer program ˝Adobe Photoshop˝. The research results show that the feeding of the caterpillars of the horse chestnut leaf miner moth affects the reduction of the assimilation potential of wild chestnut leaves. The reduction in the assimilation capacity of the leaves ranged from 0.76 % to 10.36 %, and increased with the appearance of each new generation of pest.