To comprehend the behavior of structural masonry in fire situations, it is important to understand the thermal and mechanical properties of the component materials of structural masonry (blocks, mortars, grout and coating), separately and together. This study focuses on estimating the residual mechanical properties of structural concrete blocks prisms after exposure to high temperatures through ultrasonic tests. For this purpose, two types of structural concrete blocks (6 MPa and 24 MPa) and their respective laying mortars (5 MPa and 20 MPa) were selected. Two block prisms were subjected to an ultrasonic test using exponential transducers (45 kHz) and direct ultrasonic pulse transmission. Subsequently, axial compression tests were conducted on prisms. With the increase in temperature, there was a reduction in compressive strength and ultrasonic pulse velocity (UPV) in proportion to the nominal compressive strength of the prisms, up to temperatures of 600 ℃. The correlation between residual UPV values and residual compressive strength was found not to be linear. For the prism, this correlation was better for the ultrasonic tests conducted in the longitudinal direction. In the axial direction, this correlation was too low (due to the presence of mortar), except for the polynomial trend line.