A novel carbonaceous poly(furfuryl alcohol) (CPFA) membrane was fabricated by partially carbonizing a poly(furfuryl alcohol) (PFA) layer supported on a commercial polysulfone substrate with high-concentration sulfuric acid at room temperature. Gas permeation experiments suggested that the PFA membrane became microporous after sulfuric acid treatment. ATR-IR spectra showed that the furan structure of PFA was degraded by the high-concentration sulfuric acid, forming CPFA. As compared with the PFA membrane, the CPFA membrane exhibited significantly enhanced chlorine resistance and water desalination properties. The CPFA membrane had a salt rejection of around 93.3% and a water permeability of 1.54 L·μm·m−2·h−1·bar−1. After the chlorine treatment, the CPFA membrane exhibited a salt rejection of 73.7% and a water permeability of 2.01 L·μm·m−2·h−1·bar−1, whereas the PFA membrane had a salt rejection of only 60.1% and a water permeability of 0.17 L·μm·m−2·h−1·bar−1.