Most evidence concerning cross-linguistic variation in noun bias, the preponderance of nouns in early expressive lexicons (Gentner, 1982), has come from comparisons of monolingual children acquiring different languages. Such designs are susceptible to a number of potential confounders, including group differences in developmental level and sociodemographic characteristics. The aim of this study was to quantify noun bias in bilingual Mandarin- English toddlers whose expressive lexicons in each language contained 50-300 words. Parents of fifty children (1;10-2;6) reported separately on their English and Mandarin expressive lexicons. The mean percentage of Mandarin nouns (38%) was significantly lower than the percentage of English nouns (54%) and was robust to analyses of twelve potential covariates. Analyses of the most frequently reported words suggested that lexical reduplication could be considered as a potential influence on vocabulary composition in future studies. Results suggest that characteristics of the input significantly shape early lexicons.