An industrial manganese-promoted ultrafine particle (UFP) iron catalyst for slurry phase Fischer-Tropsch synthesis was examined in a 1 dm(3) stirred tank slurry reactor under various reaction conditions as a representative of industrial practice (533-573 K, 1.5-2.5 MPa, 1.0-2.51 (STP)/g-cat h, H-2/CO=0.65-2.0). The Fe-Mn UFP catalyst showed high CO conversion and gave high yields of C-2-C-4 alkenes, partially attributed to less secondary hydrogenation of alkenes during the slurry reaction. The catalyst displayed a slow deactivation rate with time on stream. The effects of reaction conditions on the catalytic activity, hydrocarbon product distribution and the ratio of alkene/alkane were discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.