Molecules of the title compound, [(4-nitrophenyl)sulfanyl]acetic acid, C(8)H(7)NO(4)S, are linked by paired O-H* * *O hydrogen bonds [H.O 1.81 A, O.O 2.6456 (15) A and O-H* * *O 178 degrees ] into centrosymmetric dimers containing an R(2)2(8) motif. A single C-H* * *O hydrogen bond having a nitro O atom as acceptor [H* * *O 2.47 A, 3.3018 (19) A and C-H.O 147 degrees ] links the dimers into a molecular ladder, and neighbouring ladders are weakly linked into sheets by aromatic pi-pi-stacking interactions.