An advanced mechanical properties estimation with instrumented indentation technique (IIT) using spherical indenter was applied to steels used in aged bridges. First, the effect of surface polishing on the variation in indentation load-depth curve was investigated to ensure the reliability of IIT. Under suitable testing condition, mechanical properties, such as stress-strain curve, yield stress and tensile strength, of aged steels was estimated and compared with tensile test results to validate the estimation accuracy. Meanwhile, the effect of heating and cooling process simulating fire was also evaluated by the IIT. It can be concluded from the results that the IIT is useful to estimate the mechanical properties of aged steels for bridges.
