A vehicle body frame structure for an all-terrain vehicle having at least a front wheel, and including a first frame assembly and a second frame assembly. The first frame assembly includes an arm support portion and a steering shaft support portion located at a front portion of the vehicle body frame structure, for steering the front wheel. The second frame assembly is bisected from the first frame assembly; and the vehicle body frame structure also includes a suspension arm vertically swingably supported by the arm support portion.