The effects of the loading condition and the specimen geometry on the elastic-plastic crack growth in structural low-carbon steel under high cyclic stresses are investigated experimentally. The acceleration of crack growth rate, deviating from the stable relation between the rate and the J-integral range, was found to take place coincidently with the onset of the ratcheting extension of the specimen. Based on the fractographic observation, the crack growth acceleration is attributed to the incomplete reversal of plastic deformation in ratcheting extension and to the inclusion of dimple-mode fracture in crack growth. The maximum amount of crack growth acceleration through the former mechanism is predictable by considering the increase in crack-tip opening displacement. A method to evaluate the transitional behavior from stable fatigue growth to unstable fracture is proposed by introducing the concept of fatigue crack growth resistance curve.