First-principles　calculations　based　on　density　functional　theory　(DFT)　and　the　periodical　slab　model　were　used　to　study　the　adsorption　and　dissociation　of　methanol　on　the　perfect　FeS2(100)　surface.　The　adsorption　energy　and　the　geometric　parameters　on　the　different　adsorption　sites　showed　that　the　Fe　site　was　the　most　favorable　adsorption　site　and　O　atoms　were　found　to　bind　to　Fe　atoms.　After　adsorption,　the　C.　O　and　O.　H　bonds　of　methanol　were　elongated　and　the　vibrational　stretch　frequency　was　red　shifted.　The　calculation　results　proved　that　methanol　was　prone　to　decomposition　resulting　in　methoxy　groups　and　hydrogen.　We　calculated　the　adsorption　behavior　of　these　methoxy　groups　and　hydrogen　on　the　FeS2(100)　surface　and　found　that　the　Fe　sites　were　also　the　most　favorable　adsorption　sites.　A　possible　decomposition　pathway　was　investigated　using　transition　state　searching　methods:　first　the　O　-　H　bond　of　methanol　was　decomposed　producing　the　intermediate　methoxy　group　and　subsequently　the　C　-　H　bond　of　the　methoxy　group　was　broken　resulting　in　final　products　of　formaldehyde　and　hydrogen.