Ethanol and aqueous extracts ofMachilus thunbergiiSieb et Zucc (Lauraceae) used traditionally for the treatment of a variety of diseases were screenedin vitrofor MMP-1 inhibitory actions.Meso-dihydroguaiaretic acid (MDGA) from the stem bark ofM. thunbergiishowed a significant inhibition of matrix metalloproteinase (MMP)-1 in primary human fibroblasts by heat shock-induced. This study investigated the effect of MDGA isolated fromM. thunbergiion heat shock-induced premature skin aging. MDGA reduced the expression of MMP-1 at the protein level in a dose-dependent manner in heat shock-induced cultured primary human fibroblasts. Taken together, these results show that MDGA can prevent the harmful effects of heat (and/or IR) that lead to skin aging.