Differential affective processing has been widely documented for bilinguals: L1 affective words elicit higher levels of arousal and stronger emotionality ratings than L2 affective words (Pavlenko, 2012). In this study, we focus on two closely related Chinese languages, Mandarin and Cantonese, whose affective lexicons are highly overlapping, with shared lexical items that only differ in pronunciation across languages. We recorded L1 Cantonese – L2 Mandarin bilinguals’ pupil responses to auditory tokens of Cantonese and Mandarin affective words. Our results showed that Cantonese–Mandarin bilinguals had stronger pupil responses when the affective words were pronounced in Cantonese (L1) than when the same words were pronounced in Mandarin (L2). The effect was most evident in taboo words and among bilinguals with lower L2 proficiency. We discuss the theoretical implications of the findings in the frameworks of exemplar theory and models of the bilingual lexicon.