We aim to empirically examine the effects of self-directed learning on class attitude among university students, focusing on the mediating effects of social networking service (SNS)-related variables, including social networking service (SNS) addiction tendency, emotional expression through social networking service (SNS), social networking service (SNS) utilization ability, and grit. We conducted a survey with 257 university students and analyzed the collected data using the Statistical Package for the Social Sciences (SPSS) Process macro. The results of our study are as follows. First, self-directed learning demonstrated significant correlations with SNS addiction tendency, emotional expression through social networking service (SNS), social networking service (SNS) utilization ability, grit, and class attitude. Second, the social networking service (SNS)-related variables exhibited a dual mediating effect in the relationship between self-directed learning and class attitude. Third, we identified significant mediation pathways from self-directed learning to class attitude through these variables. We contribute to the literature by revealing the complex mechanisms by which SNS-related factors and grit influence students' academic behaviors. Based on these findings, we propose educational strategies to strengthen self-directed learning and provide directions for future research that emphasize both digital competency and psychological perseverance in higher education contexts.