The effect of carbon addition on the magnetostriction of Fe–Ga and Fe–Al alloys was investigated and is summarized in this study. It was found that the addition of carbon generally increased the magnetostriction over binary alloys of Fe–Ga and Fe–Al systems. The formation of carbide in the Fe–Ga–C alloys with a composition near D03 phase region decreased the magnetostriction drastically. Fe–Al–C and Fe–Ga–C alloys responded differently to thermal treatments; the magnetostriction in the quenched Fe–Al–C alloys is equal to or slightly lower than that of the slow cooled as is observed in binary Fe–Al alloy; in contrast, the magnetostriction is generally higher in quenched Fe–Ga–C alloys than slow cooled condition, consistent with the behavior of binary alloys of Fe–Ga. A significant increase in magnetostriction between 25% and 165% depending on the phase region in Fe–Ga–C alloys by quenching was observed in the A2+D03 two-phase region and D03 single phase region.