In order to observe the effect on organism DNA repair capacity after administration of Essence-Restoring Decoction (ERD), the level of peripheral lymphocyte unscheduled DNA synthesis (UDS) in 20 healthy young men, 23 healthy old men and 13 old men given ERD were detected, while the frequency of sister chromosome exchange (SCE) of mice marrow cells in 80 ICR strain male mice were detected. Ultraviolet (UV) and mitomycin-C (MMC) were used as agents to induce injury of DNA. Experimental results showed that the level of UDS in the aged person was lower than that of the young person. Comparing the level of UDS of the aged before and after medication, it was shown that the level of UDS after medication was increased, approaching that of the young. Within a range of lower doses (less than 5mg/kg weight), the SCE value of mice marrow cells raised with the increase of MMC concentration, while this values was markedly lowered in the medicated mice as compared with that of the control. It is thus suggested that ERD could enhance the DNA repair capacity and this might be a part of the mechanism of "Invigorating Kidney and retarding aging" as indicated in TCM.