The growth mechanism of hexagonal tungsten oxide (h-WO 3) nanorods is investigated using molecular dynamics simulation. The results show that cation intercalation has a great impact on the formation of h-WO 3 nanorods, reflected from the attractive interaction between the growth species (polytungstate anion, W 10O 32 4-) and crystal faces of (001) and (100). In particular, an appropriate amount of intercalated cations not only accelerate the crystal growth but also induce the formation of one-dimensional nanostructure of h-WO 3 nanorods along the direction of . An excess of intercalated cations would be unfavorable to the evolution of rod shape. Ammonium ion (NH 4 +) is found to be the most stable in a hexagonal tunnel, hence being effective in inducing the 1D morphology of h-WO 3. The main findings from the simulations are also verified by experiments.