A novel flower-like hydrated magnesium carbonate hydroxide, Mg5 (CO3)4 (OH)2 • 4H2O, with micro-structure composed of individual thin nano-sheets was synthesized using a facile solution route without the use of template or organic surfactant. Reaction time has an important effect on the final morphology of the product. The micro-structure and morphology of Mg5 (CO3)4 (OH)2 • 4H2O were characterized by means of X-ray diffractometry (XRD), field-emission scanning electron microscopy (FE-SEM). Brunauer-Emmett-Teller (BET) surface areas of the samples were also measured. The probable formation mechanism of flower-like micro-structure was discussed. It was found that Mg5 (CO3)4 (OH)2 • 4H2O with flower-like micro-structure was a novel and efficient catalyst for the synthesis of diphenyl carbonate (DPC) by transesterification of dimethyl carbonate (DMC) with phenol.