A saw blade positioning mechanism for an annular sawing machine includes a protective case, two first driven wheels, two second driven wheels, and an adjustment component. The protective case conceals a portion of an annular saw blade. The first and second driven wheels are rotatably disposed at two opposing ends of the protective case and abut against two opposing lateral sides of the annular saw blade, respectively. The adjustment component is disposed at the protective case to drive the protective case to move in the radial direction of the annular saw blade relative to the annular saw blade. The position of the protective case is adjusted with the adjustment component such that the first and second driven wheels get positioned in place synchronously with displacement of the protective case. The protective case can be demounted so that the first and second driven wheels are simultaneously removed and changed.