Three new phytoecdysteroids have been isolated from the seeds of Chenopodium quinoa and structurally identified as 20,26-dihydroxy, 28-methyl ecdysone, 20,26-dihydroxy, 24(28)-dehydro ecdysone, and 20-hydroxyecdysone 22-glycolate using serial chromatographic and spectroscopic methods. Both previously reported compounds and newly identified phytoecdysteroids were evaluated for their inhibitory effect on calf skin collagenase, as this enzyme is involved in aging skin diseases. Their effectiveness on scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals, as well as in chelating the iron metal ions was also investigated. All isolated compounds demonstrated a higher potency to inhibit this matrix metalloproteinase and to chelate the iron ion, both with respect to the number of carbonyl groups bearing their carbon skeleton, suggesting that their mechanism of action involves their ability to coordinate both ions (either the zinc ion of the catalytic domain of collagenase or the iron ion), acting as an electron donor. The DPPH-scavenging ability was hydroxyl dependent. Satisfactory results obtained from the enzyme in vitro experiment were further supported by the gel electrophoresis. These results indicate that ecdysteroids might be considered as potent chemical agents to prevent or delay both collagenase-related skin damages and oxidative stress.