Biochar　has　been　found　to　be　a　potentially　suitable　amendment　for　landfill　cover　material　and　agricultural　soil.　The　addition　of　biochar　can　improve　the　physical　(e.g.,　adsorption　capacity)　and　hydrological　properties　(e.g.,　water/gas　permeability)　of　soil.　However,　no　experimental　study　is　available　about　the　effect　of　biochar　content　(BC)　on　the　gas　diffusion　coefficient　(DP)　of　soil.　The　present　study　investigated　the　effect　of　BC　on　DP　under　different　degree　of　compaction　(DOC;　85%,　90%,　and　95%)　and　soil　air　contents　(SAC;　5%,　10%,　and　15%).　It　was　found　that　DOC　and　BC　had　negligible　effects　on　DP　when　SAC　was　low　(~　5%).　In　contrast,　when　the　SAC　was　relatively　high　(~　15%),　soil　with　DOC　of　85%　had　the　largest　DP　for　BC　ranging　from　0　to　15%　(w/w).　Only　when　the　SAC　was　large　(~　15%),　the　addition　of　biochar　generally　increased　DP.　©　2020,　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.