A general strategy to produce 2D transition metal hydroxide nanosheets is proposed here. This 'green chemistry' approach requires less equipment, includes simple operation steps and costs little. FeOOH, Co(OH)2, Ni(OH)2, Fe-Mn hydroxide, Co-Zn hydroxide and Ni-Zn hydroxide nanosheets were successfully synthesized through a mechanism of preferentially oriented growth. The produced nanosheets are ultrathin and possess large specific surface area. The representative unmodified FeOOH nanosheets exhibit potential performance for application as a positive contrast agent.