This work aims at confirming the importance of Walt Whitman s work, Leaves of Grass, in Fernando Pessoa`s poetic production. His contact with the American poet was paramount for the appearance of two of his most significant heteronyms: Álvaro de Campos and Alberto Caeiro. Whitman, who still in the mid XIX century was already a forerunner of Modernism, supposedly had great influence over the Portuguese poet s work. We will attempt to demonstrate how this influence was exercised, by establishing convergence and intertextuality points between the two authors, both as far as form and themes are concerned, observing some relevant poems in the pessonian production. We will also investigate some differences found in the comparison of the poets works. In the process, the following poems will be studied more closely: Saudação a Walt Whitman, Ode Triunfal, and Passagem das Horas by Campos, besides the poems that make up O Guardador de Rebanhos by Caeiro.