The Bridge Safety Department of Seoul Metropolitan Government has regularly conducted precise inspection and precision safety inspection to maintain the bridge's function and safety. During a precise safety inspection in 2015, oil leakage progression was found on the cable anchorage system within the stiffened girder of Nilsen Arch bridge and as a follow-up measure, the cable replacement for the cable ACD11 was carried out in order to identify the relevant cause of the oil leakage and evaluate the integrity of the existing cable. The mechanical properties and fatigue performance tests of the cable strands of bridge inservice for about 20 years and comprehensive analysis of oil leakage were carried out. They were described hereby.