MoS2 thin films prepared via sulfurization of molybdenum films have attracted great attention due to their advantage for scalable synthesis with a large area coverage. However, the MoS2 thin films are typically more resistive than their exfoliated and co-evaporation chemical vapor deposition based counterparts. The ability to modulate the electrical property of MoS2 thin films will have a significant impact on scalable device applications in electronics, sensors, and catalysis. Here, we report the tuning of electrical transport properties of large area MoS2 thin films with different oxygen plasma exposure times. The electrical transport measurements of the pristine and plasma treated samples reveal that with increasing oxygen plasma treatment, the resistance of the MoS2 thin films first decreases by almost an order of magnitude and then increases again. The x-ray photoelectron spectroscopy measurements show that the S:Mo ratio continuously decreases with increasing plasma exposure time. For a short plasma exposure time, the resistance decrease can be explained due to the creation of sulfur vacancies leaving unsaturated electrons with molybdenum (Mo) atoms which act as electron donors. With increasing plasma exposure, more sulfur vacancies and hence more Mo atoms are created, many of which get converted to insulating MoO3 resulting in an increase in the resistance of the MoS2 thin film. The results presented here are a major step forward in realizing the overreaching goals of MoS2 thin films for practical device applications.