Cochlear implants (CIs) provide children with profound hearing loss access to sounds and speech. Research on the effects of CI on speech and language development in mainland China is scarce due to the lack of standardized tests. This study aims at developing a vocabulary measure, the Mandarin Expressive and Receptive Vocabulary Test (MERVT), for pre-school children with CIs. Using responses from 102 normal-hearing preschool children, the initial vocabulary set was subjected to analyses to identify items with appropriate levels of difficulty and discrimination. Norms on 245 normal-hearing children aged 1;6 to 3;11 were later collected based on the final set of the items. Evaluation of the test's psychometric properties revealed good internal consistency. Significant correlations between the total MERVT scores and the Gesell Developmental Scale scores, between the MERVT expressive and receptive subtest scores and the total scores, and the gradual increase in MERVT scores with age, provided evidence of construct validity. Results from 29 children with CIs were also examined for evidence of the MERVT's construct validity. There was a significant correlation between these children's MERVT scores and their scores from an intelligence test. The MERVT scores increased with an increase in the duration of CI use and in chronological age. With good reliability and strong validity, the test is recommended for use in the monitoring of language development in children with CI.