PET fabric was treated by R.F. plasma of CF$_4$, and PET film as auxiliary sample was treated by same method. The treated samples were washed with boiling water in soxhlet apparatus for 4 hrs, dried at room temperature for 48 hrs, and heat treated at 15$0^{circ}C$ for 10 mins. In order to investigate the most optimum treatment condition, plasma gas pressure and treatment time were systematically changed, and the effect of Ar plasma pretreatment was examined too. The water repellent properties of plasma treated samples were evaluated by contact angle meter, and the changes of surface chemical characteristics were analyzed by ESCA. The results obtained are as follows: 1) There was a good water repellent property when plasma gas pressure is near of 0.09~0.1 torr and duration of discharge is more of 90 seconds. 2) After washing the water repellency was decreased, however, heat treatment was done it was regained about more of 50%. 3) The pretreatment of Ar plasma has an effect on durability of washing, and the best condition of pretreatment of Ar were 0.04~0.06 torr, 30~90 seconds. 4) There were correspond relationship between the PET film contact angle and the fabric water droplet rolling-off angle under same plasma treatment condition. 5) The fabric contact angle could not revealed the precise differences of water repellency of the surface, however, the measurement of water droplet rolling-off angle could be effective method. 6) According to ESCA analysis, there were prevailing -CHF- bond and a little -CF$_2$- and -CF$_3$ bond on CF$_4$ plasma treated substrate, therefore it seemed that fluorination was mainly caused by -CHF- bond.