This paper investigates the wind-induced dynamic response at design wind speed and the collapse of a mechanically-attached membrane roofing system installed on metal substrate of flat-roofed low-rise steel building, based on a wind pressure loading test using full-scale assembly specimens. Three kinds of waterproofing membranes with different mechanical properties are tested. The wind loads employed in the test are generated by using the time histories of wind pressure coefficients on the roof of a flat-roofed low-rise building with low parapets, which were obtained from a wind tunnel experiment. Both the temporal and spatial variations of wind pressures are reproduced by using three Pressure Loading Actuators (PLAs). A step-wise pressure loading test commonly employed in the conventional wind-resistant performance evaluation in Japan is also carried out for a comparative purpose. The results indicate that the fasteners connecting the disks with the metal substrate are subjected to not only vertical uplift forces due to negative wind pressures (suctions) but also horizontal forces related to the membrane deformation. The maximum value of horizontal force is nearly equal to that of the vertical force. Although the general correlation between vertical and horizontal forces is not so high, the maximum values of these forces may occur almost simultaneously. Larger the membrane deformation, larger the horizontal forces are. The horizontal forces reduce the failure loads and affect the failure modes significantly. Therefore, the effect of horizontal forces should be considered in the evaluation of wind-resistant performance of mechanically-attached membrane roofing systems. The failure load under step-wise pressure is generally smaller than that under fluctuating wind pressures. Therefore, the conventional step-wise pressure loading test can be used as a simple method for evaluating the failure load of the roofing system on the safer side.