Surface active elements in liquid metals decrease the surface tension remakably even at very low level of bulk concentration. Interstitial free elements such as oxygen, sulfur, and nitrogen are known to behave as surface active elements in liquid Fe-based alloys. However, it is not so well understood whether carbon is a surface active element or not. In the present study, the surface active nature of carbon on the Fe-Mn alloys was examined. The surface tension of the Fe-Mn alloys was investigated by using the advanced sessile drop method under a H2-Ar gas atmosphere. It was found that the surface tension decreased by increasing manganese or carbon concentrations and by increasing the temperature. The surface tension of the Fe-Mn-C alloys was successfuly described by the Langmuir adsorption isotherm. The surface adsorption of carbon at saturation was slightly decreased by increasing bulk manganese concentration. On the other hand, the adsorption coefficient of carbon was increased by increasing bulk manganese concentration.