This paper is the first systematic study on the idea of “moral vegetarianism” (daode sushi zhuyi 道德素食主義) in modern China, a concept used by Chinese people since the 1910s to categorize vegetarian practices motivated by ethical concerns rather than health. Examining historical sources including periodicals, comics, cookbooks, and intellectual writings, this paper traces the central role of evolutionary discourses and diffused Buddhist concepts such as “affective beings” in the formation of “moral vegetarianism” as an affective trans-species ethic. The paper highlights the effects of secularization in shaping the idea’s historical specificity by analyzing how the discourse of emotion, such as “universal love,” compassion, and sympathy, constituted moral vegetarianism’s core reasoning and overtook pre-modern Chinese vegetarianism’s emphasis on religious doctrines. The paper also examines shifts in moral discourses surrounding vegetarianism during the 1930s–40s nationwide “vegetarian campaigns” (sushi yundong 素食運動), wherein Confucian vegetarian ritual was appropriated by the state for wartime mobilization to shape patriotic and economically responsible citizens, while the moral vegetarian idea was stigmatized as “superstition” and marginalized. This original study foregrounds food ethics and the contestation of moral discourses in China’s modern formation, offering a crucial yet overlooked context for the modern transition of the nation's foodways and beyond.