Organic-inorganic　halide　perovskites　(OIHPs)　have　the　typical　composition　of　APbX(3),　in　which　A　is　a　cation　such　as　methlyamine　(MA)　and　formamidine　(FA)　and　X　is　a　halide　anion　such　as　Cl,　Br,　or　I.　The　mixture　at　the　A　or　X　site　in　OIHPs　provides　greatly　improved　versatility　in　their　compositions　and　therefore　allows　the　enhancement　of　their　performance　in　LEDs　and　solar　cells.　In　real　application　circumstances　and　deformable　devices,　the　mechanical　properties　of　OIHPs　are　of　great　importance.　In　this　work,　the　mechanical　properties　of　three　series　of　mixed　OIHP　single　crystals,　MAPbI(x)Br(3-x),　MAPbBr(x)Cl(3-x),　and　FA(y)MA(1-y)PbBr(3),　are　studied　by　nanoindentation.　The　results　are　summarized　according　to　the　composition　of　these　mixtures.　With　the　increase　in　the　FA　content　at　the　A　site,　the　average　Young＇s　modulus　(E)　of　FA(y)MA(1-y)PbBr(3)　decreases　greatly　from　19.2　GPa　to　11.5　GPa,　which　indicates　that　the　influence　of　organic　cations　on　the　mechanical　properties　of　OIHPs　is　as　important　as　that　of　Pb-X　bonds.　The　mixture　at　the　A　or　X　site　could　also　increase　the　hardness　(H)　and　the　wear　resistance　(H/E　ratio).　The　average　values　of　hardness　and　wear　resistance　of　MAPbI(0.1)Br(2.9)　are　almost　double　(0.63　GPa,　0.033)　the　values　for　undoped　MAPbBr(3)　(0.32　GPa,　0.017).　The　dynamic　mechanical　responses　of　the　OIHP　single　crystals　show　reduced　creep　stress　exponents　and　thus　increased　strain　rate　sensitivities　in　the　mixture　at　the　X　site,　thereby　improving　the　ductility.　The　nanoindentation　sites　are　characterized　using　a　scanning　electron　microscope　and　slip　bands　are　observed,　suggesting　the　plastic　deformation　mechanism　governed　by　the　activation　of　dislocations.