Indium tin oxide, which is used as transparent conducting layer in flexible device, is deposited on PET film by a magnetron sputtering in 300 mm wide roll-to-roll process (vacuum web coating). Sheet resistance, specific resistance and transmittance is differed by sputtering parameters such as working pressures, oxygen partial pressure, and thickness of ITO layer. ITO layer is deposited about 90 nm at roll speed of 0.24 m/min and its sputtering power is 3 kW. From the XRD spectrum deposited ITO layer is verified as amorphous. Under working pressure varied from $3{ imes}10^{-4};Torr$ to $2{ imes}10^{-3};Torr$, sheet resistance is lowest at the working pressure of $1{ imes}10^{-3};Torr$ and its value is from $110;{Omega}/{square}$ to $260;{Omega}/{square}$ at the thickness of 90 nm. Oxygen partial pressure also varies sheet resistance and is optimized at the regime from 0.2% ($1.8{ imes}10^{-6};Torr$) to 0.6% ($6{ imes}10^{-6};Torr$). In this oxygen partial pressure sheet resistance is lower than $150;{Omega}/{square}$. As ITO layer thickness increases, sheet resistance decreases down to $21;{Omega}/{square}$ and specific resistance is about $7.5{ imes}10.4{Omega}cm$ in 340 nm thickness ITO layer. Transmittance is measured at the wavelength of 550 nm and is about 90% for 180 nm thickness ITO/PET.