This paper presents a Root Cause Failure analysis for tubing API 5CT Grade J55 leakage on the well conductor. The tubing was installed in oil Well production with gas lift process and found leaked after three years in service. The leakage was reported as multiple leakages after performing an inspection. The investigation has been completed on leaked well tubing. The material conformity confirmed that the tubing material is J55 grade according to API 5 CT. Analysis on the failure mode revealed that the tubing leakage is caused by CO2 corrosion as a result of high CO2 partial pressure in the Well tubing which in the range of 7 to 30 psi at a depth range of 237.4 feet to 1818.1 feet and over 30 psi at a depth above 1818.1 feet. The CO2 corrosion is reported high because the water cut increases during the operation from 2016 to 2018. The dissolved carbon dioxide caused damage on the ID surface of the tubing in the form of pitting and mesa type attack. The Damage is also contributed by the flow inside the tubing where it is reported that the flow regime is slug where large gas bubble creates high shear stress and vibration to the tubing. This effect accelerates the metal loss where localized attach by CO2 corrosion occurs. The inclination of the tubing in well also contributes to the preferential damage on the tubing.