Nano energetic materials have attracted great attention recently owing to their potential applications for both civilian and military purposes. By introducing silicon microchannel plates (Si-MCPs) three-dimensional (3D)-ordered structures, monocrystalline MnMoO
4
with a size of tens of micrometres and polycrystalline MnMoO
4
nanoflakes are produced on the surface and sidewall of nickel-coated Si-MCP, respectively. The MnMoO
4
crystals ripen controllably forming polycrystalline nanoflakes with lattice fringes of 0.542 nm corresponding to the
(
1
¯
11
)
plane on the sidewall. And these MnMoO
4
nanoflakes show apparent thermite performance which is rarely reported and represents MnMoO
4
becoming a new category of energetic materials after nanocrystallization. Additionally, the nanocrystallization mechanism is interpreted by ionic diffusion caused by 3D structure. The results indicate that the Si-MCP is a promising substrate for nanocrystallization of energetic materials such as MnMoO
4
.