Many models of reference production suggest that speakers tend to use a reduced referential form, such as a pronoun, to signal the topicality of a particular referent, that is, the Topichood Hypothesis. However, little is known about the precise nature of the mapping between topichood and referential form and the mechanisms by which topichood affects referential form. The current study aims to address these issues by investigating how topicality influences different kinds of reduced expressions, namely, null and overt pronouns in Mandarin. We manipulated topicality using a left-dislocation structure in Experiment 1. We found that topicality increased the use of null pronouns, but not overt pronouns. This suggests that topicality may increase only the most reduced expression available in a given language. Experiment 2 examined whether the topicality effect was related to predictability. We found that participants used more null pronouns for less predictable referents. We suggest that the topicality effect could be better explained by an accessibility mechanism.