Mechanical properties variability generally has marginal influence in the seismic risk of structures, because the uncertainties governing the seismic hazard usually prevail over those concerning the materials. When the degradation process is considered, further uncertainties are introduced into the reliability problem, whose influence on the failure probability needs to be assessed. This paper aims to address this point by evaluating, in a probabilistic manner, the sensitivity of the risk estimates to a set of basic random variables governing the chloride diffusion process and the consequent rebars corrosion of a reinforced concrete bridge pier. The results highlight that the uncertainties related to the degradation process cannot be disregarded, and some basic random variables are more influential than others.