Abstract: The three-point bending tests on notched beams with different steel fibre volume fractions and different specimen sizes were conducted. The resistances to crack initiation of randomly distributed steel fibre reinforced cementitious composite (SFRC) and aligned steel fibre reinforced cementitious composite (ASFRC) were studied. Based on the load-crack mouth opening displacement curves, the influence of steel fibres on fracture properties of cementitious composites was disscussed, and the initial fracture toughness was determined by sudden reduction of linearly related coefficient. The results show that the initial fracture toughness of ASFRC is significantly greater than that of SFRC. The initial fracture toughness increases with the steel fibre volume fraction, and the increasing tendency of ASFRC tends to be stable when the steel fibre volume fraction is higher than 0.9%. The initial fracture toughnesses of SFRC and ASFRC all increase with the specimen sizes varying from 40 mm to 100 mm, and the increasing tendency is slower in ASFRC. In addition, the enhancement of ASFRC to initial fracture toughness was explained by taking into account the fact that the inclusion embedded at the crack tip of composite would change the crack tip stress intensity factor.