This research aimed to investigate the relationship between insecure attachment styles and nomophobia in emerging adult students with The mediating role of negative perfectionism. Regarding the procedure, it was a descriptive-correlation study. All Tehran universities formed the research community, and 417 people were selected as a sample in the academic year 1402 – 1403. Research questionnaires included: The revised Adult Attachment Scale (1990), the Nomophobia questionnaire (2015), and The Frost Multidimensional Perfectionism Scale (1990). The analysis method of this research is structural equation modeling, which was used to examine the causal relationships of research variables. The findings showed that the direct effect of insecure attachment styles on nomophobia was positive and significant (P = 0.001) and the direct effect of insecure attachments on negative perfectionism was also positive and significant (P = 0.001). Also, the indirect effect of insecure attachment styles with the mediating of negative perfectionism on nomophobia was positive and significant (P = 0.008). These findings show that negative perfectionism has a significant mediating role in the relationship between insecure attachments and nomophobia in emerging adult students.