The exploration of novel synthetic methodologies that control both size and shape of functional nanostructures opens new avenues for the functional application of nanomaterials. Here we report a new and versatile approach to synthesize single crystalline oxides nanorods: thermal conversion from amorphous oxides nanoparticle precursor (RuO(2)center dot xH(2)O nanoparticle precursor was used as a model system). The shape and size of RuO(2) nanorods can be well controlled by varying the heat-treatment conditions in ambient air. The mechanisms involved are the following: thermal dissociation-crystallization process, including surface diffusion, heterogeneous nucleation, and subsequent anisotropic growth into nanorods on silicon substrate governed by the Wulff construction rule. Additional experiments show also the successful conversion of IrO(2)center dot xH(2)O nanoparticle precursors into nanorods of IrO(2). Therefore, this novel approach based on the thermal conversion of amorphous nanoparticles precursor into single crystalline nanorods points at a general route for the synthesis of one-dimensional oxide nanomaterials. We have tested the functional properties of the nanorods regarding field emission and the results indicate that RuO(2) nanorods can act as excellent field emitters.