In this study, a low temperature hydro iodic acid (HI) vapor treatment of the self-assembled graphene films has been developed, and the electrical, optical, structural and morphological properties were investigated by four-point probe, UV–Visible spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). Mono-, double- and triple-layer of graphene flakes were deposited on glass substrates by using the Double Self-Assembly (DSA) process. The self-assembled graphene films were treated with HI vapors at 40 ◦C for different time intervals between 1 and 24 h. In addition, graphene deposition and HI-vapor treatment (at 40 ◦C for 1 h) was enforced three times to the same substrate. The optical transparency values of the self-assembled mono- (MGFs), double- (DGFs) and triple-layer graphene flakes (TGFs) were measured as 91, 85 and 80%, respectively (values at 550 nm). Due to the HI-vapor treatment, the sheet resistance of MGFs significantly reduced from 1.1 × 107 Ω □􀀀 1 to 2.9 × 104 Ω □􀀀 1, the transparency of the graphene films slightly reduced by 2–5%, the ID/IG ratio of the DGFs decreased from 1.01 to 0.81, while the I2D/IG ratio increased from 0.43 to 0.48 in the Raman spectrum. Thanks to its impressive reducing effect on sheet resistance, HI-vapor treatment can be a suitable method to improve the conductivity of low-cost large area graphene films.