Silicon　oxycarbide　(SiOC)　ceramics　are　increasingly　considered　as　an　emerging　class　of　materials　that　have　the　potential　for　thermal　insulation　application　because　of　their　high　thermal　resistance　and　low　thermal　conductivity.　However,　cracks　and　microchannels　are　likely　to　form　during　the　preparation　of　SiOC　ceramics,　exerting　negative　impacts　on　their　mechanical　and　thermal　performances.　In　this　study,　a　pyrolysis　heating　rate　based　pressureless　method　was　proposed　to　prepare　dense　and　crack-free　polymer-derived　SiOC　bulk　ceramics.　Then　effects　of　pyrolysis　heating　rate　on　phase　compositions　of　the　prepared　SiOC　ceramics　were　investigated.　Characterization　results　showed　that　the　bulk　density　increased　with　the　decrease　in　pyrolysis　heating　rate,　and　dense　and　crack-free　SiOC　ceramics　were　successfully　prepared　as　the　rate　decreased　to　0.5　°C/min.　Besides,　phase　compositions　were　independent　of　the　pyrolysis　heating　rate.　Moreover,　thermal　behavior　investigation　revealed　excellent　thermal　performance　of　prepared　dense　and　crack-free　SiOC　ceramics　to　1600　°C.　Though　the　geometry　of　the　bulk　ceramics　was　limited　by　the　mold　in　this　work,　the　proposed　method　is　transferable　to　other　polymer-derived　ceramics　(PDCs)　systems　to　fabricate　practical　temperature-resistant　structures　with　complex　shapes.　©　2020　Elsevier　Ltd　and　Techna　Group　S.r.l.