Using electro-polished low carbon steel specimens, the change in surface states and the incipient fatigue cracks of plain and notched specimens subjected to rotating bending stress were investigated. The main results obtained are as follows. (1) When the limit stress for macro-crack initiation σ
w1 is repeated, the amount of slip bands appearing at the root of notch is nearly equal, not only after 10
7 cycles but also at every cycle ratio, even if the maximum stress ασ
w1 at the bottom of notch is different in various radii of the notches. (2) In the specimens with various radii of the notches, the limit stress for slip bands initiation σ
ws is almost proportional to the stress σ
w1, that is, σ
ws≌(0.85∼0.9)σ
w1. (3) The incipient fatigue cracks, which appear on plain specimens after 10
7 cycles of the stress σ
w1, can hardly sustain the tensile stress statically and dynamically.
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