Charge disproportionation and magnetic order of Fe in LaSr3Fe3O10

57Fe Mössbauer measurements have been performed for LaSr3Fe3O10, which has a perovskite structure with a triple layer of FeO6 octahedra. From the temperature dependence of the Mössbauer spectra, charge disproportionation (3Fe11/3+→2Fe3++Fe5+) and magnetic order occur at 150 K, simultaneously. Mössbauer spectrum under the external magnetic fields is nearly identical to that observed from Lal/3Sr2/3FeO3, and it is suggested that LaSr3Fe3O10 is an antiferromagnet with a collinear spin structure as La1/3Sr2/3FeO3.