We investigate the structural evolution of reduced graphene oxide (RGO) sheets with carbon sp2 fractions varying from 55 to 80% using low-temperature Coulomb blockade (CB) transport. At 4.2 K, all RGO sheets exhibit a complete suppression of current (CB) below a threshold voltage V t, the value of which decreased from 3.34 to 0.25 V with increasing carbon sp2 fraction. From the temperature-dependent Vt, we calculate an effective charging energy and individual graphene domain size of 160 meV and 1.34 nm at 55% carbon sp2 fractions, respectively. These values are 20 meV and 4.18 nm at 80% carbon sp2 fractions, respectively. This implies that with increasing reduction, newly formed sp 2 domains increase the effective size of the graphene domain. For an applied voltage V > Vt, the current I follows a scaling law I ∼ [(V - Vt)/Vt]α where the scaling parameter α increases from 2.11 to 3.40 with increasing sp2 fraction, suggesting that increasing sp2 fraction creates more topological defects on the RGO. Our report provides a much desired insight into the structural evolution of RGO sheets.