Abstract The one-dimensional incommensurate modulated structure of ankangite (Ba0.827(Ti5.827V2.294Cr0.053)O16), a mineral recently discovered in China, has been studied by electron diffraction. Its average structure belongs to tetragonal system and unit cell parameters of the average structure are a= 10.2?, c=2.96?. The modulated wave spreading along direction c has the wave length of λ = 2.30c. The features of electron diffraction patterns are analysed in detail. The possible mechanism of the incommensurate modulated structure in ankangite is discussed and a modulated structure model of vacancy-displacive type is proposed. The disorder structure caused by the difference among initial phases for displacement functions from place to place is discussed.