Experimental investigations were carried out for assessing the influence of thermal loadings on the physical and mechanical properties of plain concrete after fire exposure. Cylindrical specimens were subjected to thermal loading at different temperatures inside of a muffle furnace; while cubic specimens were exposed to direct flame following the ISO 834 standard curve. For both specimens? geometries the thermal loading was applied until it reached the selected temperature which was hold for an hour. Also, in both cases, the experimental specimens were cooled in the respective furnace before any testing. Both specimens were tested for weight loss, optical microscopy and ultrasonic pulse velocity. In addition, cylindrical samples were investigated for residual compressive strength, X-ray diffraction and porosity. Control specimens were also prepared for assessing the physical and mechanical properties at room temperature. It has been observed that with the increase in the thermal loading, the physical and mechanical properties experienced significant detriment. Specifically, the results showed that the ultrasonic pulse velocity method showed an excellent performance as an indicator of concrete compressive strength and microstructural properties after fire exposure.