As　a　pilot　laboratory,　Bureau　International　des　Poids　et　Mesures　(BIPM)　organized　CCT-K7　key　comparison　of　cells　of　triple　point　of　water　(TPW),　which　20　national　measurement　standard　laboratories　took　part　in.　According　to　the　protocol　for　this　comparison,　each　participant　chose　one　calibrated　transfer　cell　and　sent　it　to　BIPM　to　compare　it　with　two　common　reference　cells.　This　comparison　at　BIPM　is　described　in　detail,　including　freezing　method,　experimental　setup　and　measurement　procedure,　comparison　results　and　corresponding　uncertainty　budgets.　The　comparison　results　indicate　that　most　cells　are　in　agreement　within　±0.15　mK.