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　(D-P)　of　soil.　The　present　study　investigated　the　effect　of　BC　on　D-P　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　D-P　when　SAC　was　low　(similar　to　5%).　In　contrast,　when　the　SAC　was　relatively　high　(similar　to　15%),　soil　with　DOC　of　85%　had　the　largest　D-P　for　BC　ranging　from　0　to　15%　(w/w).　Only　when　the　SAC　was　large　(similar　to　15%),　the　addition　of　biochar　generally　increased　D-P.