Si3N4　ceramics　were　prepared　via　gas　pressure　sintering　under　nitrogen　pressure　of　1.0MPa　at　1850　for　3h　with　Y2O3　and　MgSiN2　as　sintering　aids.　The　effects　of　MgSiN2/Y2O3　mole　ratio　and　their　total　amount　on　the　porosity,　microstructure,　mechanical　properties　and　thermal　conductivity　of　Si3N4　ceramics　were　investigated.　The　results　show　that　the　growth　of　rod-like　β-Si3N4　grains　was　more　sufficient　and　the　growth　of　abnormal　grain　decreased　with　the　increase　of　Y2O3　content　at　the　constant　total　content　of　MgSiN2　and　Y2O3.　Si3N4　ceramics　with　the　optimal　properties　were　prepared　at　a　molar　ratio　of　MgSiN2:Y2O3　of　5:2　and　the　total　amount　of　sintering　aids　of　10.5%,　having　the　bending　strength　and　thermal　conductivity　of　510MPa　and　67.01　W•m--1•K-1,　respectively.　©　2021,　Editorial　Department　of　Journal　of　the　Chinese　Ceramic　Society.　All　right　reserved.