Fly　ash　(FA)　is　one　of　the　common　supplementary　cementitious　materials　used　in　cement　and　concrete.　Because　of　the　complexity　of　morphology,　component,　hydration　and　other　factors　of　FA,　it　is　very　difficult　to　measure　the　content　of　FA　in　hardened　concrete.　According　to　the　characteristic　of　the　unburned　carbon　in　FA　neither　dissolving　in　concrete　nor　participating　in　the　chemical　reaction,　three　different　kinds　of　FA　were　used　to　prepare　FA-cement　pastes　with　different　volumes.　Then　selective　dissolution　method　and　thermal　analysis　were　used　to　quantitatively　analyze　the　content　of　FA　in　hardened　paste.　The　results　indicated　that　the　differences　of　testing　data　were　less　than　1.5%,　compared　with　the　theoretical　values　by　the　method　of　selective　dissolution　combined　with　thermal　analysis.　Therefore,　it　is　concluded　that　the　method　of　selective　dissolution　combined　with　the　thermal　analysis　can　measure　the　content　of　FA　in　hardened　FA-cement　system　more　accurately.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.