Many investigations about superalloys and coatings have been done in the laboratory, but evaluating the degradation condition of hot section components during service is still important not only for repair and reuse but also for outage prevention. Time dependent degradation for 1st stage blades of gas turbine was investigated. The degradation analysis for used blades was divided into microstructure changes by position in the blade and mechanical tests. In the microstructure analysis, the rafting and coarsening of γ', MC decomposition and TCP(Topologically closed packed) phase formation occurred and progressed with increasing service time, and especially at the leading and trailing edge of top layer which should be a check points for used blades. Stress-rupture test results of 25,000 and 52,000 EOH(Equivalent Operating Hours) for used blades were also compared with serviced time and position in each blade.