Sir Philip Sidney is the first English poet-critic. Although his literary works exhibit a trace of his poetic thoughts about the crafts and functions of poetry, his importance to the history of literary theory rests on a single work, Defence of Poesie. To defend poetry and protect the poets, Sidney refutes the attacks imposed on poetry. The paper lays emphasis on three parts: theoretical source of Sidney's poetic thoughts, Sidney's understanding of the function of the poet and function of poetry.