Fischer-Tropsch synthesis was carried out at atmospheric pressure in a fixed-bed microreactor at temperatures and weight hourly space velocities (WHSV) ranging from 513 to 533 K and 5 to 25 h(-1), respectively, over hybrid catalysts (physical mixtures) containing Co-Ni-ZrO2 and sulfated-ZrO2 catalysts. The sulfated-ZrO2/Co-Ni-ZrO2 catalyst weight ratios (SZ/CN) ranged from 0 to 3, whereas sulfate concentrations in sulfated-ZrO2 catalyst (sulfate loading) ranged from 5 to 15 wt %. Fischer-Tropsch synthesis over Co-Ni-ZrO2 catalyst alone produced a maximum C-4 hydrocarbon selectivity of 14.6 wt % at a temperature of 523 K and WHSV of 15 h(-1). There was an impressive increase in C-4 hydrocarbons selectivity to a maximum of 32.4 wt % when catalyst HB5,1 (SZ/CN of 1 and sulfate loading of 5 wt %) was used. This catalyst also gave an extremely high selectivity for isobutane (maximum of 10.6 wt % of total hydrocarbon products) as compared to 0.1 wt % obtained with Co-Ni-ZrO2 catalyst. A time-on-stream study on catalyst HB5,1 showed a decrease in activity of this catalyst with reaction time. In contrast, the use of hybrid catalyst HB5,0.5 (SZ/CN of 0.5 and sulfur loading of 5) where the overall sulfur content was low resulted in almost no deactivation. However, the activity obtained in the case of catalyst HB5,0.5 was lower than that obtained for catalyst HB5,1 but was much higher than that for Co-Ni-ZrO2 catalyst. On the other hand, for hybrid catalysts HB5,2 and HB15,1, which had high overall concentrations of sulfur, there was no activity at all. The results show that interactions brought about by close proximity of Fischer-Tropsch catalyst active sites and acid sites produce favorable effects when the overall sulfur content in the hybrid catalyst is low.