The width-thickness ratio of the rotation capacity of the HSB800 steel flexural members are evaluated in this study. First of all, the properties of high-performance steel are analyzed from the tension coupon test - SS400, SM490, HSB800. By the result, high-performance steel have the three properties - the high yield ratio, the low modulus of elasticity strain-hardening, and the low strain at tension stress. The rotation capacity of the HSB800 steel flexural members are evaluated using F.E. program. By the F.E result, the HSB800 steel flexural members are not satisfied in the current code that rotation capacity, R>3 in compact section. Based in the experiment and theories, this study suggested limiting the width-thickness ratio of HSB800 steel satisfied in the current code. So, the limitation of width-thickness ratio of the HSB800 steel are conservative than the width-thickness ratio in the code.