The　correlation　between　the　thermal　transport　properties　and　microstructural　evolution　of　amorphous　alloys　is　crucial　for　their　application　in　thermal　insulation.　Herein,　Fe48Cr15Mo14C15B6Y2　amorphous　alloy　with　low　thermal　conductivity　of　7.74　W/mK　was　investigated　to　reveal　this　relationship.　Isochronal　annealing　experiment　demonstrates　a　limited　increase　in　thermal　conductivity　at　temperatures　below　the　crystallization　temperature　(T-x1　=　620.7　degrees　C),　despite　the　occurrence　of　structural　relaxation　or　partial　crystallization,　which　is　ascribed　to　the　conflicting　variations　of　electron　and　phonon　contributions　with　increasing　temperature.　At　annealing　temperature　above　T-x1,　the　two　contributors　start　to　cooperate,　leading　to　abrupt　enhancement　of　thermal　conductivity.　On　the　other　hand,　isothermal　annealing　experiments　reveal　that　at　temperatures　below　T-x1,　the　thermal　conductivity　is　independent　of　annealing　time.　Although　full　crystallization　can　be　induced　slowly　by　annealing　at　600　degrees　C,　the　thermal　conductivity　keeps　nearly　constant　at　8.35　W/mK,　which　is　attributed　to　additional　scattering　by　a　newly　introduced　phase　interface.　Moreover,　grain　growth　upon　prolonged　annealing　at　850　degrees　C　results　in　a　slow　increase　in　thermal　conductivity,　which　asymptotically　saturates　at　12.44　W/mK.　The　obtained　results　demonstrate　the　potential　of　the　Fe　-based　amorphous　alloy　as　thermal　insulator　and　form　a　basis　for　future　works　aiming　to　shed　further　light　on　the　evolution　of　amorphous　alloy　and　the　sluggish　effect　of　transformation　kinetics.　(C)　2020　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.