Background <p>This study aimed to estimate the prevalence of chronotypes among male prisoners in China and to examine the relationship between chronotype, insomnia, and depressive symptoms in this population.</p> Methods <p>A total of 1609 male inmates participated in this cross-sectional study by completing the Morning and Evening Questionnaire-5 (MEQ-5), Insomnia Severity Index (ISI), and Patient Health Questionnaire-9 (PHQ-9). Age, time served, insomnia, and depressive symptoms were compared across chronotypes. Binary logistic stepwise regression was used to analyze factors influencing depression. Additionally, a simple mediation model incorporating MEQ-5, ISI, and PHQ-9 was analyzed, with age controlled as a covariate.</p> Results <p>The prevalence of morning type (MT), neutral type (NT), and evening type (ET) was 47.2%, 46.7%, and 6.1%, respectively. Being an ET was significantly associated with younger age and increased symptoms of insomnia and depression (<i>P</i> &lt; 0.05). The relative risk of depression was 2.970-fold higher (95% CI, 1.724 to 5.116; <i>P</i> &lt; 0.001) for ET compared to MT. Mediation analysis revealed that insomnia partially mediated the relationship between chronotype and depression, while the direct effect of chronotype on depression was also significant (accounting for 50.51% of the total effect).</p> Conclusions <p>The prevalence of ET is relatively low among male prisoners. Resetting ET tendencies may reduce depressive symptoms in this population.</p>