MreB, a homolog of eukaryotic actin, participates in morphogenesis, cell division, cell polarity, and chromosome segregation in prokaryotes. In this study, a yellow fluorescent protein conjugate (YFP-MreBVp) was generated to investigate the behavior of MreB in merodiploid strain SC9 of the enteropathogen Vibrio parahaemolyticus. Under normal growth conditions, YFP-MreBVp formed helical filaments with a pitch of 0.64 ± 0.09 µm in about 85% of exponential-phase cells, and different clusters, relaxed coils, and ring configurations were observed in a small proportion of the cells. Overexpression of YFP-MreBVp substantially altered the structure of the MreB cytoskeleton and resulted in swollen and pleomorphic cells. Disturbing the activities of penicillin-binding proteins or adding magnesium suppressed the morphological distortions. These results indicate that mislocalization of cell wall-synthesizing machinery was responsible for morphological abnormality. By expressing YFP-MreBVp in the ectopic host bacterium Escherichia coli, shrinkage, fragmentation, and annealing of MreBVp filaments were directly observed. This work revealed the dynamic pattern of the localization of YFP-MreBVp in V. parahaemolyticus and its relationship to cell morphogenesis, and the YFP-MreBVp-E. coli system may be used to investigate the dynamic spatial structures of the MreB cytoskeleton in vivo.