The precipitation of carbides in Fe-C-Nb alloy has been investigated using field ion microscopy and atom probe tomography. Analyses show that niobium carbide precipitates already exist in the state quenched from 1240degreesC. Detailed structural analysis of the states aged at 750degreesC reveals the existence of two types of niobium carbide precipitates with different concentrations of carbon. In addition, the direction of the habit plane for the matrix/niobium carbide interface has been determined. Copyright (C) 2004 John Wiley Sons, Ltd.