Although　ammonia　as　a　carbon-free　fuel　is　regarded　as　an　energy　source　worthy　of　significant　development,　how　to　address　the　shortcomings　of　its　poor　combustion　properties　has　been　a　hot　topic　of　research.　Hydrogen　enrichment　is　a　promising　solution　to　improve　the　combustion　properties　of　ammonia,　but　at　the　same　time,　the　potential　explosion　risk　will　inevitably　be　raised.　In　this　paper,　the　effects　of　hydrogen　volumetric　fraction　(chi)　in　NH3/H-2　on　the　NH3/H-2/air　deflagrations　were　experimentally　investigated　in　a　rectangular　duct　with　an　end-opening　at　an　initial　pressure　and　temperature　of　101　kPa　and　298　K,　where　chi　was　varied　from　0.1　to　0.9.　Results　demonstrate　that　flame　propagation　and　overpressure　profiles　inside　and　outside　the　chamber　depend　on　chi.　Buoyancy　plays　a　significant　role　in　flame　propagation　at　chi　=　0.1.　More　prominent　deformation　of　the　flame　front　propagating　toward　the　closed　end　(CE)　was　observed　in　the　experiments　with　higher　chi　s.　Helmholtz　oscillations　of　the　flame　occurred　in　all　tests,　which　resulted　in　pressure　oscillations　with　a　decreasing　frequency　as　chi　was　increased.　Acoustically　enhanced　combustion　of　NH3/H-2/air　remained　at　the　CE,　appeared　when　chi　＞=　0.7,　and　acoustic-type　oscillations　of　the　internal　explosion　overpressure　and　a　pressure　peak　of　p(2)　formed　in　these　tests.　The　amplitude　of　p(2)　dropped　as　chi　varied　from　0.7　to　0.9.　A　proportional　relationship　between　the　highest　explosion　overpressure　inside　the　chamber　(p(max))　and　the　square　of　the　laminar　burning　velocity　of　NH3/H-2/air　(s(l)(2)).　When　chi　＞=　0.3,　a　dominant　pressure　peak　(p(ext))　caused　by　the　external　explosion　appeared　in　the　external　overpressure　profiles,　and　its　amplitude　increased　as　chi　varied　from　0.3　to　0.9.