This research analyzㄷㄴ the discourse in The Letters of Denise Levertov and William Carlos Williams through the lens of Aristotelian rhetoric― especially ethos and epideictic rhetoric. During an 11-year span of their long acquaintance and correspondence, October 1951 through June 1962, their principal epistolary passion was poetry and poetics. They led separate domestic lives―Williams in the Rutherford, New Jersey area and Levertov in New York, Maine, and Mexico. A remarkable thing about their relationship is that they did not become alienated or indifferent, and their effective communication was built on ethos and epideictic rhetoric. Levertov trusted Williams’s ethos from the beginning of their correspondence; meanwhiles Williams’s estimation of Levertov grew with the years. Williams praised Levertov’s poems for their rhythmic structure, objectivism, social consciousness, and keen perception about her immediate surroundings, but he occasionally advised her to cut some lines. Thereby, Williams contributed to drawing the best from Levertov. For Levertov, the process was a way to fulfill her dream as a poet; for Williams, it was a way to find a promising new poet and to mentor her as established poet. This research will illuminate an example of about how a mentor can help his/her mentee in developing their potential as an artist through effective communication.