In English, positions of lexical stress in disyllabic words are associated with word categories, that is, nouns tend to be more stressed on the second syllable. This phenomenon was called stress typicality effect in previous studies, which found that English native speakers were sensitive to this effect. As an extension of previous research, the present study investigated the stress typicality effect in native Chinese speakers who learn English as a second language. Both visual grammatical classification and lexical decision tasks were administered to adults, as well as to adolescents. The results revealed that Chinese adolescents were not sensitive to stress typicality effect in English, while adults were, demonstrating the developmental trajectory of acquiring stress typicality effect in Chinese ESL learners. Key Words: grammatical category; lexical stress; stress typicality effect; orthography