<p>The study examines the impact of English L2 exposure on Mandarin L1 lexical abilities in school-age children learning English as a foreign language. While previous research has shown L1 lexical deficiency in children living in a society where the majority language is children’s L2, whether such deficiencies extend to children in a majority-L1 society is still uncertain. The study analyzed data from four cohorts of third-grade Mandarin L1 children (<i>N</i> = 467) with 7-year separation between the first and the last cohorts, focusing on various domains of their Mandarin lexical abilities: oral vocabulary, character recognition, rapid automatized naming, nonword repetition, and phonological awareness. English L2 exposure was indexed by the composite scores of cumulative and current out-of-school exposures, validated by their association with standardized English vocabulary tests. The findings reveal no significant relationships, linear or curvilinear, between English L2 exposure and Mandarin L1 lexical performance across the various lexical domains and across the four cohorts of participants, except phonological awareness, which was positively related with English L2 exposure in two cohorts. Overall, the findings do not support the notion that increased exposure to English L2 leads to cost in L1 lexical abilities in a majority-L1 society.</p>