Abstract: Self-weight has a significant influence on the fracture properties of beams under three-point bending (TPB). However, the influence of initial crack mouth opening displacement (CMOD_ini) caused by self-weight was rarely considered in previous research on concrete fracture properties based on TPB beams. To investigate the influence of CMOD_ini on the fracture properties of TPB beams, a calculation formula of CMOD_ini, effective crack length (a_c) and unstable fracture toughness (K_IC^un)considering the influence of CMOD_ini are presented. The calculated results of the formula were compared with the experimental data of specimens of different sizes and initial crack-depth ratios. The results indicate that CMOD_ini is slightly influenced by the specimen sizes. The influence of the self-weight on CMOD_ini, ac and K_IC^un is less than 5% even if the specimen size is 2200 mm×550 mm×240 mm and the initial crack-depth ratio is 0.4. CMOD_ini is greatly influenced by the initial crack-depth ratio. The influence increases with the increase of the initial crack-depth ratio. Moreover, the influences of the self-weight on CMOD_ini, a_c and K_IC^un are 24.26%, 1.73% and 17.31%, respectively, when the specimen size is 1143 mm×305 mm×76 mm and the initial crack-depth ratio is 0.818. Therefore, the influence of CMOD_ini caused by the self-weight of TPB beams should be taken into account when both the specimen size and the initial crack-depth ratio are large.