An organic-inorganic hybrid antimony(III) oxalate (C₅H₆ON)₂[Sb₂O(C₂O₄)₃] has been successfully obtained by simultaneous combination of π-conjugated 4-hydroxypyridine and (C₂O₄)^2– group with stereochemical active Sb(III) cation. The compound features a layered structure, and the equatorial planes of SbO₆ units, π-conjugated (C₂O₄)^2– and (C₅H₆ON)⁺ groups are closer to a planar arrangement, representing strong structural anisotropy that favors a large birefringence. As expected, (C₅H₆ON)₂[Sb₂O(C₂O₄)₃] exhibits a large birefringence of 0.279 at 546 nm. Structural and theoretical analyses indicate that the combination of multiple π-conjugated units is a feasible approach for designing and exploring new superior birefringent materials.