The aim of this experimental study was to evaluate the effect of fire flame exposure with different intensities of firing on the mechanical properties of a high strength concrete (HSC). Many variables were encountered in this study. Two mixes of 80 MPa target compressive strength (1:1.22:2) with 3% Nano-Metakaolin and the other with 5% were used. Two types of coarse aggregate were used (natural crushed gravel and crushed dolomite rock with maximum size of 14mm). The specimens were moist cured for 28 days, air-dried in the laboratory to firing at ages 90 days at three temperature levels (400, 600, 800)oC and for three exposure periods (1, 1.5 and 2 hours). Different methods were used to cool specimens. The reduction values of compressive strength for all mixes ranged between (2-69.5)% at 400oC, (8-72)% at 600oC and (10-85)% at 800oC , the reduction values of splitting tensile strength were (9-43.2)%, (17-50)% and (39-76)%, and the reduction values of flexural strength were (51.7-84.8)%, (52.8-87) %, (53.6-87.8)%, respectively.