The size of chemically modified graphene nanosheets is a critical parameter that affects their performance and applications. Here, we show that the lateral size of graphene oxide (GO) nanosheets is strongly correlated with the concentration of graphite oxide present in the suspension as graphite oxide is exfoliated by sonication. The size of the GO nanosheets increased from less than 100 nm to several micrometers as the concentration of graphite oxide in the suspension was increased up to a critical concentration. An investigation of the evaporation behavior of the GO nanosheet solution using inkjet printing revealed that the critical temperature of formation of a uniform film, T(c), was lower for the large GO nanosheets than for the small GO nanosheets. This difference was attributed to the interactions between the two-dimensional structures of GO nanosheets and the substrate as well as the interactions among the GO nanosheets. Furthermore, we fabricated organic thin film transistors (OTFTs) using line-patterned reduced GO as electrodes. The OTFTs displayed different electrical performances, depending on the graphene sheet size. We believe that our new strategy to control the size of GO nanosheets and our findings about the colloidal and electrical properties of size-controlled GO nanosheets will be very effective to fabricate graphene based printed electronics.