To elucidate the molecular dynamics of HP1β in mouse preimplantation embryos, we examined the localization, dynamics, and mobility of HP1β in the (pro)nucleus by live cell imaging. Time-lapse observation revealed that the chromatin association of HP1β is regulated in a cell cycle-dependent manner. HP1β was localized in the interphase nucleus and was dynamically dissociated from the nucleus during the metaphase stage. The HP1β assembly and clustered heterochromatin structure were both found in the nuclei of 2-cell and later-stage embryos. Moreover, fluorescent recovery after photobleaching analysis implied that HP1β is more freely mobile in the pronucleus of the 1-cell embryo than in the 4-cell nucleus. These results suggest that the chromatin configuration may be regulated by the stability and mobility of chromatin-associated proteins including HP1β during early embryonic stages.