To explore the mediating effect of fear of missing out on the relationship between alexithymia and mobile phone addiction. Methods: A cluster random sampling method was employed to select 554 college students from four colleges and universities in Wuhan, Hubei Province, China, between April and May 2022. The participants completed the Toronto Alexithymia Scale-20 (TAS-20), the Mobile Phone Addiction Index (MPAI), and the Fear of Missing Out Scale (FoMOs). Descriptive statistics and Pearson’s correlations were computed using SPSS 26.0, and the intermediary effect was examined using PROCESS 3.5. Results: The total scores for alexithymia, mobile phone addiction, and fear of missing out were (58.24±12.62), (46.90±13.54), and (22.81±6.95), respectively. Pearson’s correlation analysis revealed that alexithymia was positively correlated with mobile phone addiction (r=0.69, P<0.01), fear of missing out (r=0.66, P<0.01), and fear of missing out was positively correlated with mobile phone addiction (r=0.70, P<0.01). The mediation analysis, controlling for the effect of sex, showed that alexithymia had a significant direct predictive effect on mobile phone addiction (β= 0.73, P<0.01). Furthermore, fear of missing out partially mediated the relationship between alexithymia and mobile phone addiction (effect size=0.31, 95% CI 0.231～0.354), accounting for 42% of the total effect. Conclusion: Alexithymia contributes to mobile phone addiction directly, as well as indirectly through the mediating effect of fear of missing out.