Microsorum grossum (Polypodiaceae), locally called metuapua'a, is one of the most frequently used fern species in Polynesian traditional medicine. Fronds or rhizomes of this species are common ingredients of popular medicine recipes to cure various ailments. M. grossum frond and rhizome extracts contain, as their main bioactive components, phytoecdysteroids such as 20-hydroxyecdysone, known to have many interesting biological activities and considered to be adaptogenic compounds [1]. The skin-active effect of M. grossum extract was investigated in two ways on human dermal fibroblasts: a transcriptomic study with c-DNA array for gene expression modulation and a Stress Induced Premature Senescence (SIPS) test. The total extract of M. grossum up-regulates Heme Oxygenase 1 (HO1), an enzyme which protects cells from oxidative stress and which is responsible for skin photoimmunoprotection. The present paper also reports that premature senescence of human skin induced by repeated UV irradiations can be prevented by an ecdysteroid fraction of M. grossum. Our data indicate that extracts of M. grossum could protect skin against oxidative stresses and suggest that they could be used as innovative active cosmetic ingredients.