Retinal ganglion cell line (RGC-5) has been widely used as a valuable model for studying pathophysiology and physiology of retinal ganglion cells in vitro. However, the electrophysiological characteristics, especially a thorough classification of ionic currents in the cell line, remain to be elucidated in details. In the present study, we determined the resting membrane potential (RMP) in RGC-5 cell line and then identified different types of ionic currents by using the whole-cell patch-clamp technique. The RMP recorded in the cell line was between −30 and −6 mV (−17.6 ± 2.6 mV, n = 10). We observed the following voltage-gated ion channel currents: (1) inwardly rectifying Cl− current (ICl,ir), which could be blocked by Zn2+; (2) Ca2+-activated Cl− current (ICl,Ca), which was sensitive to extracellular Ca2+ and could be inhibited by disodium 4,4’-diisothiocyanatostilbene-2,2’-disulfonate; (3) inwardly rectifying K+ currents (IK1), which could be blocked by Ba2+; (4) a small amount of delayed rectifier K+ current (IK). On the other hand, the voltage-gated sodium channels current (INa) and transient outward potassium channels current (IA) were not observed in this cell line. These results further characterize the ionic currents in the RGC-5 cell line and are beneficial for future studies especially on ion channel (patho)physiology and pharmacology in the RGC-5 cell line.