Iron-based　sulfides　have　been　deemed　as　an　appealing　anode　material　for　lithium-ion　batteries　(LIBs)　and　sodium-ion　batteries　(SIBs)　for　their　high　theoretical　capacity　and　low　cost.　However,　their　practical　application　is　limited　by　drastic　volume　expansion　during　cycling　and　low-intrinsic　electronic　conductivity.　In　this　work,　we　report　a　FeS2/Fe7S8-rGO　composite　synthesized　via　a　facile　solvothermal　method　as　an　LIB/SIB　anode.　The　FeS2/Fe7S8-rGO　anode　exhibits　an　excellent　Li-storage　capacity　of　514　mAh　g(-1)　at　2.0　A　g(-1)　after　3000　cycles　and　a　Na-storage　capacity　of　650　mAh　g(-1)　at　0.2　A　g(-1)　after　250　cycles,　respectively.　The　rGO　matrix　is　deemed　responsible　for　providing　good　electron　conduction　and　alleviating　volume　expansion　during　cycling.　The　electrokinetic　analysis　confirms　a　large　portion　of　intercalational　pseudocapacitance　as　a　major　contribution　to　the　superior　rate　performance.　In　situ　X-ray　diffraction　further　reveals　details　of　a　combined　intercalational　and　conversional　Li-ion　storage　mechanisms　in　this　Fe-sulfide-based　anode.　Finally,　density　functional　theory　calculations　suggest　that　there　exists　a　synergistic　effect　at　the　heterointerface　between　FeS2　and　Fe7S8　to　promote　electrokinetics.