The concrete, red brick and iron were used for thickness determination of multi-layer materials. The 133Ba, 137Cs and 60Co radioactive source were used energy at 356, 662 and 1173 keV for gamma rays transmission measurement technique. The dispersive X-ray fluorescence spectrometer (EDXRF) was used to confirmed the chemical composition with all sample. The thickness determination of multi-layer materials can be written in the form of a matrix and solves the matrix of equations using the Cramer’s rule. The thickness of experimental values was compared with high accuracy vernier caliper instrument. The results show that the thickness of experimental values are good agreement with vernier caliper and the relative difference percentage (% RD) is not over 4%.