Deposition processes of lithium in solid polymer [poly(ethylene oxide) (PEG)8+LiClO4] and gel [PEO8+propylene carbonate(PC) +LiClO4] electrolytes, as well as in the liquid (PC+LiClO4) one, were observed in situ using an optical microscope and their difference is discussed. It was confirmed that the dendritic growth of lithium, which appeared in the liquid electrolyte, is suppressed in the solid polymer due to the immobility of the electrolyte molecules, although non-uniform coverage of the cathode was observed because of its low conductivity. In contrast, the gel electrolyte possessed advantages of both the liquid and solid electrolytes, resulting in a smooth and uniform deposition in the current density region up to 2.0 mA cm(-2).