Hole expansion using a flat-bottomed cylindrical punch was carried out to clarify the fracture behavior of high-strength steel sheets by changing the initial hole diameter, d₀. Experimental results showed that the hole expansion ratio, λ, became larger as the initial hole diameter, d₀, increased. Moreover, the fracture site around the hole shifted considerably with the initial hole diameter, d₀, in the case of high-strength steel sheets with high r-value. On the other hand, the analytical results exhibited poor coincidence with experimental ones when the initial hole diameter was small, whereas good correlation was observed with a large initial hole diameter. As a result, it was clarified that plastic deformation behavior during stretch flange forming performed using a flat-bottomed cylindrical punch is influenced not only by the planar anisotropy of the mechanical properties of steel sheets but also by the initial hole diameter.