The present paper is devoted to the study of wall paint of the late 16th - early 17th centuries with zoomorphic image of St. Christopher located at the Assumption Cathedral (which became UNESCO object in 2017) of the town-island of Sviyazhsk and is the first investigation of Russian murals of this time. The work includes archaeometry examination of wall paint with portable X-ray fluorescent spectrometer (pXRF) for the pigment’s determination and by optical microscopy and scanning electron microscopy (OM-SEM) for fresco structure study with some notes of the appearance of an unusual image of the saint and history of this fresco creating. The analysis found the ancient masters used red and yellow ocher, umber, ―green earth‖, blue smalt as colorants. The discovered cinnabar, minium, lead white, paints with chromium, titanium and nickel are evidence of restoration work of the different time. As studies have shown some regions of fresco have several painting layers indicating alterations in original image of Saint Christopher with the dog head. Results of plaster examination showed that it was made from dolomite raw material. In addition, white scurf near the cracks in the wall has been studied by X-ray diffraction (XRD). Separation of calcium and magnesium structures due to degradation process of the fresco base was revealed on the OM-SEM-pictures.