In recent years, research focusing on childhood has reported that communication difficulties in autism spectrum disorder (ASD) are related to the social reciprocity difficulties inherent to ASD, as well as severe social anxiety and decreased verbal fluency. However, there have been no reports regarding these correlations and causal relationships in adulthood. The aim of this study was to reveal the effects of social reciprocity, social anxiety, and letter fluency on communicative behaviors in adults with ASD (n = 33, aged 18-43 years, mean age = 27.88 years) and to compare these to typically developing (TD) adults (n = 35, 19-40 years, mean age = 28.03 years). We validated a model using structural equation modeling in which social reciprocity not only directly affected communicative behaviors, but also indirectly affected communicative behaviors mediated by social anxiety and verbal fluency. The results of the structural equation modeling showed that communicative behaviors patterns differed between the ASD and TD groups, as the ASD group had high goodness of fit with the hypothesis model while the TD group had low goodness of fit. These findings signify that in ASD, in addition to problems in social reciprocity, social anxiety (fear) is a risk factor for worsening communicative behaviors difficulties.Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.