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Development of new high-performance electrode materials for in lithium ion batteries (LIBs), especially the anode materials, has been under intense research during the past decade. The design of new electrode materials to a great extent depends on how the lithiation front propagates into the anode material. Therefore, revealing the atomic scale lithiation mechanism is central to unfolding the performance of electrode materials during the operation of LIBs. Although recent studies of in situ TEM LIBs [1][2] have revealed morphology evolution, structure and chemical changing in the anode materials during the electrochemical reaction, there is currently lack of critical knowledge about the atomistic mechanisms of dynamical lithiation.In the present work, taking advantage of an aberration-corrected scanning transmission electron microscopy (STEM), we show that the dynamic lithiation process of anode materials with atomic resolution can be revealed. Atomically resolved imaging of the lithiation process in SnO 2 nanowires illustrated that at the very initial stage of lithiation, lithium ions preferred to diffuse along [001] direction in the {200} planes, which introduced the lattice expansion and dislocations. The movement, reaction and generation of ] 1 1 1 [ b mixed dislocations effectively facilitated lithium ion insertion into the crystalline interior. At the later stages of lithiation, the Li-induced amorphization of rutile SnO 2 and the formation of crystalline Sn particles in an amorphous matrix were observed. In situ high resolution TEM imaging revealed that the morphological evolution and mobility of the interface between the crystalline Sn and amorphous Li x Sn were orientation-dependent during lithiation.