The effects of process conditions on Fischer-Tropsch Synthesis (FTS) product distributions were studied using a fixed-bed microreactor and a Co-Mn/CNT catalyst. Cobalt and Manganese, supported on Carbon Nanotubes (CNT) catalyst were prepared by a Strong Electrostatic Adsorption (SEA) method. CNT supports were initially acid and thermally treated in order to functionalize support to uptake more Co clusters. Catalyst samples were characterized by Transmitted Electron Microscope (TEM), particle size analyzer, and Thermal Gravimetric Analysis (TGA). TEM images showed catalyst metal particle intake on CNT support with different Co and Mn loading percentage. Performance test of Co-Mn/CNT in Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed micro-reactor at different pressures (from 1 atm to 25 atm), H2/CO ratio (0.5-2.5), and reduction temperature and duration. The reactor was connected to the online Gas Chromatograph (GC) for product analysis. It was found that the reaction conditions have the dominant effect on product selectivity. Cobalt catalyst supported on acid and thermal pre-treated CNT at optimum reaction condition resulted in CO conversion of 58.7 and C5+ selectivity of 59.1. © 2020 by the authors.