In　this　study,　the　effect　of　Iron　Ore　Tailings　(JOT),　as　fine　aggregate　in　mortars,　on　microstructure　and　compressive　strength　with　14　days　was　observed　on　mortar　specimens.　The　replacement　ratios　for　JOT　as　fine　aggregate　were　60%　and　100%.　Pore　structure　parameters　were　measured　with　the　instrument　of　MIP　and　calculated　with　corollary　software.　Situations　of　interface　between　aggregates　and　hard　cement　pastes　were　observed　by　FEI　quanta　200　SEM.　Consequently,　it　was　seen　that　JOT　can　improve　mortar＇s　compressive　strength　because　of　tighter　interface　between　aggregate　and　hard　cement　paste　and　enhanced　porous　structure　related　to　the　finer　structure　of　JOT　comparing　to　reference　sand.