Background: Prelinguistic communication complexity refers to the use of different communication forms such as eye gaze, gestures and vocalisations and the degree to which these forms are coordinated and how directed to a communication partner. To date, little is known about the relationship between prelinguistic communication complexity and expressive language in minimally verbal autistic children. Aims: To test the hypothesis that prelinguistic communication complexity predicts expressive language 12 months later in autistic children and explore whether there are any differences in specific prelinguistic intentional communicative behaviours that are related to later expressive language levels. Methods & Procedures: This longitudinal study examined 37 minimally verbal autistic children (29-71 months old). The Communication Complexity Scale (CCS) was used to measure participants' prelinguistic communication behaviours, which were extracted from a semi-structured play interaction at Time 1. The Chinese Communicative Development Inventory (CCDI) was used to examine participants' expressive language at Time 1 and Time 2 (12 months later). According to Time 2 vocabulary size, participants were divided into two groups: Low CCDI, between 0 and 62 words, and High CCDI, more than 100 words. Linear regression was used to examine the relationship between early prelinguistic communication complexity and later expressive language. Binary logistic regression was used to determine which of the early communication behaviours were uniquely significantly related to later expressive language levels. Outcomes & Results: There was a significant positive relationship between prelinguistic communication complexity and expressive language 12 months later, even after controlling for age and concurrent language. Findings revealed a group difference in the frequency of gesture and vocalisation combinations between the Low and High CCDI groups at Time 1. Gesture-vocalisation combinations also predicted better expressive language levels at Time 2. Conclusions & Implications: Our findings suggest that it may be beneficial to incorporate different complex communication behaviours into prelinguistic intervention targets for minimally verbal autistic children. The CCS hierarchies can be used as a reference for the intervention goals of minimally verbal autistic children. These findings highlight the importance of targeting gesture and vocalisation combinations when autistic children transition from single prelinguistic communication behaviours to multimodal behaviours.