Objective To explore the level and related factors of alexithymia in adolescents with mood disorders, and to provide references for targeted intervention. Methods A convenience sample of 198 adolescents with mood disorders was investigated using a general information questionnaire, the Toronto Alexithymia Scale, the Gross Emotion Regulation Questionnaire, and the Perceived Social Support Scale. Results The sample scored (62.47±14.02) points for alexithymia, with the incidence of alexithymia being 61.1%. The alexithymia score was negatively correlated with the score of cognitive reappraisal in emotion regulation and the score of perceived social support, whereas positively correlated with the score of expressive suppression (all P<0.05). Multiple linear regression analysis showed that gender, parents′ educational level, parental divorce, cognitive reappraisal, expressive suppression, and perceived social support were the influencing factors of alexithymia in adolescents with mood disorders (all P<0.05), explaining 81.5% of the total variance. Conclusion Adolescents with mood disorders report a relatively high level of alexithymia. Attention should be paid to adolescents whose parents′ have low education level, those whose parents have divorced, and those with poor social support, instructing them to adopt cognitive reappraisal strategies and reduce expressive suppression, resulting in alleviating alexithymia.