The main objective of this research was the charac terisation of the fracture toughness of concrete mortars exposed to high temperatures by using notched specimens in three point bending tests. The specimens have different lengths and were heated at different temperatures ranging from room temperature up to 900°C. The experimental test results obtained are closed with those reported by the literature, it shows tha t beyond approximately 300°C, the fracture loads decrease strongly with the rise in heating temperat ure. However, between the room temperature (25°C) and 300°C, we recorded an increase of the fr acture load. Two methods using the experimental critical load were applied to calculat e the fracture toughness of concrete mortars: an analytical method based on the mechanics of continu ous medium theory and a numerical approach using finite elements method. The numerical modelli ng has then been validated, discussed and compared with analytical solution. Comparison between the experimental results and the theory predictions was quite good.