Lithiation kinetics of a Si-C composite anode for high-capacity lithium-ion batteries were investigated through in-situ lithiation with electrochemical C-V measurements using a focused ion beam. Here, we found in the lithiation procedure that Li migrates sequentially into carbon (C), nanopores, and silicon (Si) in the Si-C composite. In the first lithiation step, Li was intercalated inside C particles while spreading over the surface of the C particles. The second lithiation process occurred through the filling of nanopores existing between electrode particles that consisted of the Si-C composite. The nanopores acted as a Li reservoir during the pore-filling process. Finally, the Si particles were litheated with a volume expansion of 173%, corresponding to a 400% volume expansion of 25wt.% Si particles included in the composite anode. The nanopores did not accommodate a large volume expansion of ~400% in Si particles, because pore-filling lithiation occurred before the Si lithiation in the charging process.