Abstract: An electro-abrasive polishing process of the inner surface of pipes to an extra-smooth mirror finish comprises a preliminary-polishing process and a subsequent mirror-finishing process. The preliminary-polishing process is continued until the roughness of the inner surface of the small-diameter pipe is reduced to at least 0.5 .mu.m Rmax or less by electro-abrasive polishing process of the inner surface of the small-diameter pipe by inserting a preliminary-polishing tool electrode comprising a core electrode wrapped with a non-woven nylon sheet in the small-diameter pipe to be polished and passing a small amount of current through the electrolyte between the small-diameter pipe that serves as the anode and the tool electrode that serves as the cathode and, at the same time, by mechanically polishing the inner surface of the small-diameter pipe by rotating the tool electrode and axially reciprocating it or the small-diameter pipe relative to each other.