Ser-10 phosphorylation of histone H3 is revealed to be relative to chromosome condensation at prophase during mitosis. In this report, we demonstrate using immunofluorescence microscopy that the subcellular distribution of the Ser-10 phosphorylated histone H3 was similar to that characteristic of chromosomal passenger proteins during the terminal stages of cytokinesis. Co-immunoprecipitation indicates that the Ser-10 phosphorylated histone H3 is associated with the aurora B, and both of the proteins were compacted into a complex with special ternary structure located in the centre of the midbody. When the level of the Ser-10 phosphorylated histone H3 was reduced by RNA interference, the cells formed an aberrant midbody and could not complete cytokinesis successfully. This evidence suggests that Ser-10 phosphorylated histone H3 is a chromosomal passenger protein and plays a crucial role in cytokinesis.