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.