A modern serpentine belt is designed to last around 100,000 miles of driving. Over time, the friction, heat, and corrosion result in the wear of the serpentine belt.  To be on the safe side, experts suggest that you replace the serpentine belt every 50,000 to 60,000 miles to avoid unnecessary problems.  If the serpentine belt is installed with a self-tensioning device, you will need to ask the mechanic to replace the tensioner of the serpentine belt when it needs to be replaced.