Two-dimensional　(2D)　organic–inorganic　hybrid　perovskites,　benefiting　from　their　natural　anisotropy　of　quantum-well　motifs　and　optical　properties,　have　shown　remarkable　polarization-dependent　responses　superior　to　the　3D　counterparts.　Here,　for　the　first　time,　multiwavelength　polarization-sensitive　detectors　were　fabricated　by　using　single　crystals　of　a　guanidine-based　2D　hybrid　perovskite,　(BA)2(GA)Pb2I7　(where　BA+　is　n-butylammonium　and　GA+　is　guanidium).　Its　unique　2D　quantum-well　structure　results　in　strong　crystallographic-dependence　of　optical　absorption.　Strikingly,　our　crystal-based　photodetector　exhibits　a　prominent　photocurrent　dichroic　ratio　(Imax/Imin)　of　∼2.2　at　520　nm,　higher　than　the　typical　2D　inorganic　materials　(GeSe,　∼1.09,　PdSe2,　∼1.8).　In　addition,　notable　dichroic　ratios　of　1.29　and　1.23　at　405　nm　and　637　nm　are　also　created　for　the　multiwavelength　polarized-light　detection.　The　prominent　detecting　performances,　including　low　dark　current　(1.6×10−11　A),　considerable　on/off　ratio　(∼2×103),　high　photodetectivity　(∼3.3×1011　Jones)　and　responsivity　(∼12.01　mA　W−1),　make　(BA)2(GA)Pb2I7　a　promising　candidate　for　polarized-light　detection.　This　work　sheds　light　on　the　rational　engineering　of　new　2D　hybrid　perovskites　for　the　high-performance　optoelectronic　device　applications.　©　2021　Wiley-VCH　GmbH