Poly(N-vinylcarbazole) (PVK) was sulfonated with acetyl sulfate. SIMS and XPS measurements of the sulfonated PVK show that the sulfonation occurs on the carbazole moiety and that the degree of sulfonation (DS) increases linearly with the ratio of the sulfonating agent to PVK. The DS of PVK could be controlled within a range from 12% to 28% by varying the reagent ratio. GPC measurements demonstrate that the molecular weight of PVK did not change substantially after sulfonation. UV-vis and photoluminescence spectra indicate that the sulfonation caused little change in the electronic structure of the PVK molecules but reduced significantly its photoluminescence quantum efficiency.