The electrodeposition process of Li metal in 1.0M LiTFSI–ionic liquid (N-methoxymethyl-N-methylpyrrolidinium) bis(trifluoromethane-sulfonyl) imide was observed in situ by optical microscope. Morphological variations of electrodeposited Li dendrite and its growth rate were examined and the ionic mass transfer rate in the vicinity of the electrode surface was discussed. Once the dendrite starts to grow, its length is proportional to the square root of time. This indicates that the Li+ mass transfer rate affects its growth. Dendrite growth process can be classified into two regions depending on its growth rate: the initiation period and the growing period with swinging behavior probably caused by residual stress.