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Polarized-light photodetectors are the indispensable elements for practical optical and optoelectronic device applications.Two-dimensional(2D)hybrid perovskite ferroelectrics,in which the coupling of spontaneous polarization(Ps)and light favors the dissociation of photo-induced carriers,have taken a booming position within this portfolio.However,polarized-light photodetectors with a low detection-limit remain unexplored in this 2D ferroelectric family.In this work,the high-quality individual crystals of a 2D perovskite ferroelectric,BA2CsPb2Br7(1,where BA+is n-butylammonium),were used to fabricate ultrasensitive polarized-light detectors.Its unique bilayered structural motif results in quite strong elec-tric and optical anisotropy with a large absorption ratio of αc/αa ≈ 3.2(λ = 405 nm).Besides,the presence of ferroelectric Ps also endows high built-in electric field along the polar c-axis that favors photoelectric activities.Under an extremely low detectable limit of 40 nW/cm2,the detector of 1 exhibits a notable dichroism ratio(Iphc/Ipha ≈ 1.5),a large responsivity of～39.5 mA/W and a specific detectivity of～1.2 × 1012 Jones.Moreover,crystal-based devices of 1 also exhibit a fast response speed(～300 μs)and excellent anti-fatigue merits.This work highlights great potentials of hybrid perovskite ferroelectrics toward polarized-light photodetection.