Abstract: A series of potassium modified Fe-Mn catalysts were prepared by hydrothermal method and applied to the catalytic synthesis of light olefins from CO hydrogenation. The catalyst samples were characterized by SEM, TEM, XRD, H₂-TPR and FT-IR techniques. Results showed that the prepared sample particles were spherical with 50~70 nm size and the carbonyl and hydroxy groups were observed on their surfaces. The bulk composition was mainly Fe₃O₄ before the reaction. Fe₅C₂ and MnCO₃ were formed after the reaction. The prepared samples showed high activity and olefin selectivity under the given reaction conditions. Using the sample S₃ (Fe:Mn:C₆:K=3:1:5:0.10), the CO conversion and the olefin productivity reached 95.02% and 62.86 g/m³ (H₂+CO), respectively. Compared with the catalyst prepared with co-precipitation method, the S₃ catalyst had lower CH₄ selectivity(13.88%) and CO₂ selectivity(13.98%).