The separation of Co(II) from Ni(II) in a sulfate solution across a hollow fiber membrane containing the sodium salt of Cyanex 302 dissolved in kerosene was studied. The Co(II) was simultaneously re-extracted into a strip phase containing H2SO4 in another hollow fiber membrane. Experiments were conducted to determine the effects of the feed pH (4.55.5), carrier concentration (0.10.4mol/dm3), strip acidity (0.12mol/dm3), and flow rates of the three phases (200 approximate to 600cm3/min). The percent of each metal ion extracted was found to increase with increasing feed pH, Na-Cyanex 302 concentration, and feed flow rate in the extraction module. Na-Cyanex 302 extracted Co(II) preferentially over Ni(II) under identical extraction conditions. Increasing the strip acidity and strip phase flow rate increased the recovery of Co(II) by the re-extraction module. The effect of the flow rate of the organic phase on the percent extraction and re-extraction of Co(II) were negligible. The separation of Co(II) from Ni(II) in sulfate solution was achieved using 0.3mol/dm3 Na-Cyanex 302 as extractant and 2mol/dm3 H2SO4 as stripping solution in HFMCs during a 2h extraction. At a feed pH of 5, the percent extraction and recovery of Co(II) were 84.6% and 43.7% (Ni/Co<0.05 in strip phase), respectively. The extraction efficiency and recovery of Co(II) using one-stage HFMC experiments were better than those using two-stage HFMC experiments.