Thin films of LiyV2O5(0<y<1) were made by reactive dc magnetron sputtering of V followed by electrochemical treatment in LiClO4. X‐ray diffractometry showed an orthorhombic structure that varied from nanocrystalline (n‐X ) for unheated substrates to polycrystalline (p‐X ) for substrates at 180 °C. Optical absorption was measured at 0.3<&lgr;<2.5 &mgr;m. The semiconductor bandgap lay fixed at ∼0.5 &mgr;m forp‐X  LiyV2O5and appeared blue‐shifted in proportion withyforn‐XLiyV2O5. At &lgr;>0.5 &mgr;m there are absorption peaks associated with V4+ions both forp‐Xandn‐Xmaterials, and a broad absorption feature forp‐XLiyV2O5that is tentatively ascribed to electron hopping in the crystallographicbdirection. The absorption goes up for increasedy, as expected from the higher V4+density.