Bilinguals can be proficient in oral language without necessarily knowing how to read and write in at least one of their languages. Literacy has been shown to affect language processing in monolinguals. In the present study, we test if literacy affects grammaticality judgments for Cantonese-English bilinguals who varied in Chinese literacy abilities. There are grammatical differences between oral Cantonese and written Chinese (e.g. modal verb placement). We compared response times for Chinese sentences that were either congruent or incongruent in spoken and written grammaticality. We found that for some incongruent sentences, proficient readers had significantly slower response times than congruent sentences. Unproficient readers were not affected by the grammaticality of the written form. These results show that literacy within a language can impact spoken language processing.