The word decadence tends to denote a sense of decline or decay, specifically in regard to moral standards. Critics of The Duchess of Malfi often characterize it as a decadent play due to the sensationalism and violence of the story. There is decadence as well in the fact that the integrity of the duchess is contrasted with her immoral and power-hungry siblings, Duke Ferdinand and the cardinal.

The alleged decadence of the play is easy enough to identify. The violence alone is shocking, from the grotesque spectacle of the wax corpses set up to terrorize the duchess during her imprisonment to her on-stage murder by strangulation. There is also the disturbing incest subtext: Duke Ferdinand's interest in the duchess goes beyond wanting her estate. He gives hints of desiring her sexually as well, giving his antipathy towards her secret second marriage an element of jealousy.

Within the play, decadence is prominent among the aristocracy as represented by the duchess's wicked brothers. Duke Ferdinand wants both the Duchess and her property. The cardinal keeps a mistress, despite his religious vocation and has no compunctions about committing murder to suit his own ends. This is meant to contrast with the goodness of the duchess, making her ultimate destruction by these forces all the more horrific.

Bosola, though not of the same social class as these two men, is also rather decadent in his amorality: he knows what he's doing is evil, but does it anyway. Only after the duchess dies does he change and decide to turn his violence upon his employers, though whether or not this redeems him is debatable.