Both hydrothermal and solvothermal reactions have been employed to chemically tune the polymorphology of functional materials, such as ZnO, ZnS, BaCO3, magnesium salts, copper salts, and lithium niobate. Novel self-assembled nest-like Mg-5(CO3)(4)(OH)(2)center dot 4H(2)O microspheres are formed without any organic additive or catalyst. Malachite [Cu-2(OH)(2)CO3] with a hierarchical sphere-like architecture and lindgrenite [Cu-3(OH)(2)(MoO4)(2)] with a hollow and pricky sphere-like architecture have been synthesized via a simple and mild hydrothermal route. Uniform hexagonal pencil-like BaCO3 whiskers have been synthesized by the chemical reaction of barium chloride and urea via a facile hydrothermal route. The solvothermal route has also been successfully demonstrated to the synthesis of cube-shaped lithium niobate and complex ZnO. Our results demonstrate that hydrothermal or solvothermal reactions can be used as a versatile route to the chemical synthesis of tuning polymorphology of functional materials.