Previous studies suggest that cognitive ambiguity, such as that in categorical judgments, increases response latency. However, whether or not perceptual ambiguity for bistable stimuli, in which two perceptual interpretations are mutually competitive, also cause an increase in perceptual latency remains unknown. In this study, reaction times were measured for the judgment of the perceived direction of a two-frame bistable rotational apparent motion stimulus, while manipulating the angle of rotation to control the magnitude of ambiguity. Our results show that the response time for perceptually ambiguous rotation angles (～45 deg) was only slightly longer than that of unambiguous angles (～20 deg). In contrast, response times obtained for very small angles, where motion signal weakness made the percept ambiguous, were much longer. These findings suggest that an effect of perceptual ambiguity generated by bistable stimuli on perceptual latency is very small, if at all.