In 2001, European Union decided the principle of a European global navigation satellite system and signed later on with ESA the Galileo constellation agreement. The deployment strategy of the constellation is foreseen to be done partly with the Ariane 5 ES launcher jettisoning, two by two, four Galileo Satellites on the same orbit. Choice has been made to inject upper stage on a graveyard circular orbit located 300 km below the Galileo operational one. Thus, the risk of the operational Galileo orbit interference by the upper stage at long term has to be dealt with. Indeed, the orbital parameters of the stage will be naturally modified by terrestrial potential, sun and lunar interaction and solar radiation pressure. Mainly, eccentricity's modification has to be tracked to prevent operational Galileo's orbit interference. This paper will report the estimation of stability issues for the final orbit of the Ariane 5 upper stage in Galileo mission.