Why was the sonnet attractive to the poets of the twentieth century such as Wilfred Owen, Robert Frost, W. H. Auden and Seamus Heaney? Why is it that they cared about the form in a period often dominated by unrhymed free verse? This paper quests for the answers to those questions by analyzing stylistic features of the modern sonnets of W. H. Auden and Robert Frost, and by revealing similarity between those modern poet` and John Keats`s sonnets. Keats established a coherent maturity of his sonnets that highlights man`s existential ability to stay in uncertainties and doubts in reality. The sonnet became for the poet a place to reify and reconcile a conflict between the poetic ideal and his reality. That was an unprecedented thematic mode throughout the entire sonnet tradition. As Keats had discerned, the modern poets valued the sonnet`s capability to reify opposites and to represent a sonnet persona battling its way through the problems of self and reality. Eventually, this paper reveals the vast potential of Keats`s sonnets for the twentieth-century sonnets. It intends to draw fresh attention not only to the modern sonnets but also to the modernity of Keats`s sonnets.