The subject of this diploma thesis is a painting on canvas, made in the tempera technique, by the Croatian painter Marijan Detoni (1905-1981). The painting is owned by the Academy of Fine Arts in Zagreb, and before coming to the Department of Conservation and Restoration of Art, it was kept in the Academy's Fundus. The painting was stored on an improvised wooden shelf, in a room with lots of light and with large oscillations in temperature and humidity, without proper equipment to regulate microclimatic conditions. The previous storage conditions of the painting are reflected in the current state, which is visible at first glance. The painting was created as a student work of Marijan Detoni in 1926/1927. in the class of Ljubo Babić. Under the expert guidance of mentor red. prof. mr. art. Tamara Ukrainčik, required conservation-restoration work was carried out on the painting and the accompanying wooden decorative frame. The structure of the diploma thesis is divided into several parts: theoretical and research part, making of trial simulations of the painting and practical part. The first research part describes the historical and artistic circumstances of the painting, binders used in the making of contemporary tempera and use of tempera in the production of easel paintings of the 20th century. In the second part, several smaller technical and stratigraphic simulations of the painting „Dječak“ were made, with the aim of performing consolidation, additions to the deficiencies in the base layer and retouching tests. Next part of the thesis - the conservation and restoration works consists of practical procedures carried out on the painting. It is followed by conclusions and insets. Conservation-restoration works consisted of the surface cleaning of the face and the back of the painting, additions to the defects in the base layer, consolidation of the painting, stretching on the new underframe, retouching and cleaning, additions in the base layer, retouching of the decorative frame. The work was accompanied by written documentation, photo documentation, instrumental and laboratory analyzes of samples, performed in the premises of the Department of Conservation and Restoration of Art and the Faculty of Textile Technology in Zagreb. The works were carried out in order to preserve the painting and decorative frame from further deterioration, and at the same time its aesthetic and artistic integrity was restored.