Abstract: A process for producing Bi-based oxide superconductor single crystals by the floating zone method is disclosed, which comprises using a feed rod of an oxide comprising a formulation of metallic elements represented by the following general formula:Bi.sub.p Sr.sub.q Ca.sub.r Cu.sub.2 O.sub.ywherein2.00< p< 2.18, 1.87< q< 2.00, 0.9.ltoreq. r.ltoreq. 1.0,and y is a positive number, in a moving rate of said rod of from 0.1 to 0.35 mm per hour in the side where crystals are accumulated, in which preferably, in the initial stage of the formation of crystals, the diameters of the rod-like crystals to be accumulated are changed in the wavelike state, and more preferably, in the middle stage of the subsequent formation of crystals, the amount of change thereof is gradually decreased.