By using the strategy of pre-assembly chlorosulfonation applied to a linker precursor, the first sulfonated zirconium metal-organic framework (JUK-14) with twodimensional (2D) structure, was synthesized. Single-crystal Xray diffraction reveals that the material is built of Zr 6 O 4 (OH) 4 (COO) 8 oxoclusters, doubly 4-connected by angular dicarboxylates, and stacked in layers spaced 1.5 nm apart by the presence of sulfonic groups. JUK-14 exhibits excellent hydrothermal stability, permanent porosity confirmed by gas adsorption studies, and shows high (> 10 À 4 S/cm) and low (< 10 À 8 S/cm) proton conductivity under humidified and anhydrous conditions, respectively. Post-synthesis inclusion of imidazole improves the overall conductivity increasing it to 1.7 × 10 À 3 S/cm at 60 °C and 90 % relative humidity, and by 3 orders of magnitude at 160 °C. The combination of 2D porous nature with robustness of zirconium MOFs offers new opportunities for exploration of the material towards energy and environmental applications.