Love Medicine is the debut novel of Chippewa writer Louise Erdrich, the winner of the 2021 Pulitzer Prize for Fiction.On the basis of Michel Foucault's theory of discourse, this article examines the voice battle between the two American Indian heroines in the novel, pupil Marie Lazzarre and Sister Leopolda, who both aspire to be a saint. Marie, though muted and disempowered at first, by unveiling Leopolda's lies and fraud, relinquishes her Catholic-saint identity, achieves harmony in her Self, regains her free voice, and finally becomes a real saint. Conversely, the initially sonorous and dominant Leopolda, after denying her Indian roots, persecuting her tribal people, cheating the nuns and her parishioners, turns out to be a fake saint, consequently losing her voice and power. By probing into the two women's conflicts, the paper unfolds that behind their voice battle lies the contradictions between Indian holistic ecological ideology and Euro-American values which compete for discourse and power within the postcolonial context. It also contends that, for the oppressed Native Americans, retaining Indian ethnicity and strengthening cultural bonds could be the right way to deconstruct the dualistic power hierarchy and have their voices heard.