Porous　silicon　nitride　(Si3N4)　ceramics　were　fabricated　by　compression　molding　and　slip　casting　methods　using　petroleum　coke　as　pore　forming　agent,　and　Y2O3-Al2O3　as　sintering　additives.　Microstructure,　mechanical　properties　and　gas　permeability　of　porous　Si3N4　ceramics　were　investigated.　The　mechanical　properties　and　microstructure　of　porous　Si3N4　ceramics　prepared　by　compression　molding　were　better　than　those　which　were　prepared　by　slip　casting　method,　whereas　slip　casting　method　is　suitable　for　the　preparation　of　porous　Si3N4　ceramics　with　higher　porosity　and　excellent　gas　permeability.