The initial geometries of FenO+m(n+m=4) clusters are built by using the "binomial" scheme. And 12 stable isomers are obtained by optimization and frequency analysis based on the density-functional theory GGA (PW91) and the all-electron numerical basis set. The binding energies, the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, and the magnetic moments of all the stable isomers are determined and analyzed. It is found that Fe—O bonds are important for stabilizing the FenO+m clusters, and that the total magnetic moments of the isomers are mainly dependent on the magnetic moment of iron atoms and the arrangement of the magnetic moments of the atoms.