Hierarchical tungsten carbide (WC) micro-/nanocrystals were synthesized by thermal treating a single-source precursor of the tungstate-based inorganic–organic hybrid compound in a sealed quartz tube at 1000°–1050°C. The hybrid precursor was synthesized by an acid–base reaction of H2O-moistened H2WO4 and n-octylamine in a nonpolar solvent. The X-ray diffraction results indicated that the product obtained at 1050°C for 2 h consisted of a hexagonal WC phase, and the products obtained at temperatures lower than 1000°C had other phases (e.g., α-W2C, W or β-W40.9N9.1) besides the major phase of hexagonal WC. The scanning electron microscopy observations indicated that the hexagonal WC obtained at 1050°C consisted of hierarchical microparticles with a size range of 4–18 μm, and the above microparticles were porous aggregates of WC nanoparticles with crystal sizes of 100–250 nm. The newly developed process could achieve pure WC materials at relative low temperatures using a single-source precursor, and the porous and hierarchical WC micro-/nanoparticles would have potential applications in catalysis and superhard composites.