This paper focuses on how to improve the characteristics of multi-walled carbon nanotube (MWCNT) sheet transparent, conductive films (TCFs), such as their sheet resistance (Rs) and optical transparency (T), for TCF electrodes. In this work, MWCNT sheets under went an acid treatment in HNO3 to reduce the Rs of the MWCNT sheet. The Rs of the MWCNT sheets is largely dependent on the immersion time in the acid solution. We achieved a sheet resistance of 450 Ω/sq with 90% optical transmittance at a wavelength of 550 nm for an optimized MWCNT sheet. The highly conductive, transparent and flexible thin film prepared from the MWCNT sheets is expected to be applicable to flexible electronics.