Large-area sheets are highly desirable for fundamental research and technological applications of graphene. Here we introduce a modified chemical exfoliation technique to prepare large-area graphene oxide (GO) sheets. The maximum area of the GO sheets obtained can reach ∼40000 μm². We found that the GO area is strongly correlated with the C−O content of the graphite oxide, which enables the area of the synthesized GO sheets to be controlled. By simply changing oxidation conditions, GO sheets with an average area of ca. 100−300, ca. 1000−3000, and ∼7000 μm² were selectively synthesized. For transparent conductive film applications, thin GO films were fabricated by self-assembly on a liquid/air interface and reduced by HI acid. We found that the sheet resistance of the reduced GO (rGO) films decreases with increasing sheet area at the same transmittance because of the decrease in the number of intersheet tunneling barriers. The rGO film made from GO sheets with an average area of ∼7000 μm² shows a sheet resistance of 840 Ω/sq at 78% transmittance, which is much lower than that (19.1 kΩ/sq at 79% transmittance) of a rGO film made from small-area GO sheets of ca. 100−300 μm², and comparable to that of graphene films grown on Ni by chemical vapor deposition.