To propose a new non-destructive assessment procedure for historic Suga-yarns using the “Kawabata Evaluation System (KES)”, compression resilience (RC) was compared with tensile breaking strain, which is traditionally used to measure mechanical properties of yarns. Modern raw silk yarns dyed with tannic acid and iron mordant were degraded artificially and used as a model of historic Suga-yarns. The tensile breaking strain of model yarns decreased over a 70-days degradation period, so did the RC. The mechanical properties of model yarns were categorized into “Strong”, “Weakened” and “Poor” in the order of decreasing mechanical properties. Since the SEM observations showed no damage in the morphology of yarn surfaces after compression by the KES compression tester, it was found that the compression test is a better and nondestructive evaluation method for yarns than tensile testing. The historic Suga-yarns exhibited approximately 20% - 40% of RC, and less than 7% of the tensile breaking strain. Their physical condition was classified as “Weakened” and “Poor”. This suggests that mechanical condition evaluated on the basis of model yarns can be applicable to historic Suga-yarns.