Capturing　the　long-term　performance　of　concrete　must　be　underpinned　by　a　detailed　understanding　of　the　pore　structure.　Mercury　intrusion　porosimetry　(MIP)　is　a　widely　used　technique　for　pore　structure　characterization.　However,　it　has　been　proven　inappropriate　to　measure　the　pore　size　distribution　of　cementitious　materials　due　to　the　ink-bottle　effect.　MIP　with　cyclic　pressurization-depressurization　can　overcome　the　ink-bottle　effect　and　enables　a　distinction　between　large　(ink-bottle)　pores　and　small　(throat)　pores.　In　this　paper,　pressurization-depressurization　cycling　mercury　intrusion　porosimetry　(PDC-MIP)　is　adopted　to　characterize　the　pore　structure　in　a　range　of　cementitious　pastes　cured　from　28　to　370　days.　The　results　indicate　that　PDC-MIP　provides　a　more　accurate　estimation　of　the　pore　size　distribution　in　cementitious　pastes　than　the　standard　MIP.　Bimodal　pore　size　distributions　can　be　obtained　by　performing　PDC-MIP　measurements　on　cementitious　pastes,　regardless　of　the　age.　Water-binder　ratio,　fly　ash　and　limestone　powder　have　considerable　influences　on　the　formation　of　capillary　pores　ranging　from　0.01　to　0.5　mu　m.