An investigation of the syngas conversion to light olefins over manganese promoted iron and cobalt catalysts supported on silicalite-1 has been carried out. The addition of manganese to iron catalysts improves the olefin selectivity in syngas conversion. The XRD and Mossbauer results show that manganese reduces the particle size of iron oxide and thereby makes carburization difficult. Hagg carbide phase was found to be responsible for alkane formation and olefins are preferentially obtained in the presence of some oxides of Fe(+ 3). The addition of manganese to silicalite-1 supported cobalt catalyst was found to improve the CO conversion but the olefin selectivity was slightly decreased by the presence of manganese.