This article provides a review of previous studies that have examined the effects of orthography on establishing contrastive phonological representations in second language acquisition and presents results from an original study on Mandarin speakers' production of English stops investigating how the presence of orthography affects the production of phonological categories that involve allophony. English voiceless stops are canonically represented as aspirated [p[superscript h], t[superscript h], k[superscript h]] in word-initial/stressed onset positions but are realized as unaspirated [p, t, k] following /s/ and in unstressed, non-initial onset positions. The results of our imitation experiment showed that Mandarin speakers failed to correctly imitate the unaspirated allophones when presented with written input, and this orthographic effect was stronger with nonwords than with real words. These results are best explained by an orthography effect mediated by phonological awareness and prior linguistic experience.