Fischer-Tropsch synthesis (FTS) using a Co-Mn/oxidized diamond (O-Dia) catalyst was compared among a fixed bed reactor (FBR), a trickle bed reactor (TBR), and a slurry phase reactor (SPR). For TBR and SPR, hexadecane was employed as a solvent. Regardless of the reactor, the addition of 10 mol% of Mn to Co/O-Dia catalyst greatly increased CO conversion without changing selectivity to C-5 + liquid products. The highest initial CO conversion was obtained with FBR. However, with an increase in the time on stream, CO conversion decreased, due mainly to the accumulation of high molecular weight hydrocarbons (wax) on the catalyst bed. Although with TBR the initial CO conversion was 5 % lower than that with FBR, at a feed rate of the solvent from 3 to 12 mL/(g-catalyst h), CO conversion did not decrease during a prolonged run. SPR maintained the initial CO conversion for 24 h on stream, but the CO conversion was half of that with TBR. From these findings, we propose that TBR is the most appropriate reactor type for FTS.