As a poet Castillo has authored several works, including Otro Canto (1977) The Invitation (1979), Women Are Not Roses (Arte Publico, 1984), and My Father Was a Toltec (West End Press, 1988). Her works primarily communicate the meaning and revelations we discover in various experiences. Her poem, Women Don't Riot, explores the tribulations of womanhood, but Castillo daringly uses the lines of this poem as her "offense, rejection" (line 49–50 of the poem) of the idea that she will sit quiet.
She often intermingles Spanish and English in her poetry, like in her collection of poems entitled I Ask the Impossible. The hybrid of languages that she creates is poetic and lyrical, using one language to intrigue another as opposed to a broken "Spanglish".