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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 similar to 40000 mu m(2). 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 similar to 7000 mu m(2) 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 similar to 7000 mu m(2) shows a sheet resistance of 840 Omega/sq at 78% transmittance, which is much lower than that (19.1 k Omega/sq at 79% transmittance) of a rGO film made from small-area GO sheets of ca. 100-300 mu m(2), and comparable to that of graphene films grown on Ni by chemical vapor deposition.