This paper describes the condition of the painted decorations in Osiris chapel and identifies their original materials and implemen-tation techniques by studying the stratigraphic structure. It includes information on the accumulation of soot layers as the most effe-ctive deterioration factor in the chapel. In addition, it assesses and documents the condition. Investigations were carried out using optical microscopy (OM), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. The results indicated that the blue pigment revealed Egyptian blue (Cuprorivaite), the green pigment was Egyptian green, the red pigment was red ochre, and the yellow pigment was yellow ochre. Furthermore, the used plaster layer is consisted of gypsum, the vaulted ceiling is constructed by sandstone, and the walls were built from fine crystalline limestone. The accumulated soot was noticed as black particles under the optical microscope, which showed as dark gray composed of graphite according to XRD that was com-posed of carbon as EDX result and graphite according to XRD. The hydrophobic coatings in the presence of external agents could trigger multiple deterioration mechanisms. The documentation of the wall paintings' condition was done via Autocad and Photoshop layers.