Atlas deer Cervus elaphus barbarus was reintroduced in Tazekka National Park in 1994 to help restore the natural state in the regions of the Middle Atlas and Rif mountains. A study of its diet in this area was recommended by the National Strategy for ungulates in order to get data to assess the feasibility of a subsequent release. So our aim was to study the diet of Atlas deer and its seasonal variation. Faeces were collected in Atlas during 2013–2014 in Bab Klati 520-ha reserve located in the west of the Tazekka National Park. Faecal samples were micro-histologically analysed based on a reference epidermis catalogue of all existing plants in the reserve. Poaceae species, the main representatives of the herbaceous category, were consumed at 28%, 37% and 43% of the diet in autumn, winter and spring, respectively. In summer, the consumption of Poaceae did not exceed 2%, presumably because of their limited availability. Pteridium aqualinium was consumed especially in summer (6%). Shrubs were represented by three main species: Ulex boivinii, Cytisus triflorus and Lavandula steochas. Consumption of U. boivinii was high in autumn (41%) and spring (31%) and low in winter (16%) and summer (6%). As for C. triflorus, the consumption was maximal in winter (30%), average in autumn (19%) and spring (18%) and lowest in summer (2%). Lavandula steochas was consumed mainly in autumn (8%). In the summer, trees were the main components of the diet and were represented by the oak species Quercus faginea (61%), Q.rotundifolia (13%) and Q.suber (5%). Our analysis revealed dramatic changes in the diet of Atlas deer in Morocco from one season to the other, indicating that this animal is able to change its foraging strategy based on its needs, and on the changing availability of various plants in the environment.