Present study is focused to study chemico-mineralogical characterization of a century old three brick samples collected from Patan city of Kathmandu valley, Nepal using X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic techniques. The mineralogical phases existed in all three clay brick samples used to analyze in this study by XRD-patterns are found to be of quartz, cristobalite, mullite, feldspars and different clay minerals, mostly of mica minerals from the analysis of XRD patterns. The presence of the mullite phase in all three fired clay bricks was fired at high temperature of 1100°C or more from both the XRD and FTIR analyses.