The present invention provides an alcohol extract of Ajuga taiwanensis Nakai ex Murata exhibits significant effects on inhibiting the senescence in human WI-38 lung fibroblasts and human dermal fibroblasts. Moreover, the alcohol extract of A. taiwanensis is able to suppress the expression of the cofilin-1, a protein involved in actin dynamics and cell morphology and found to be increased in senescent cells. Suppression effect of cell senescence by this herb extract is more efficient in mild concentration without over-inhibition of cell viability and growth.