Motivational drivers and emotions that students experience play an important role in the process of learning a new language (L2). This has been recognised by researchers and educators, and extensive research has been conducted in recent decades to examine the psychological and emotional factors involved in L2 learning. However, two ubiquitous epistemic emotions, namely, boredom and curiosity, remain underexplored in the L2 research literature. This study addresses this gap. It performed a series of statistical tests to examine the relationship between these two epistemic emotions and L2 motivation. Specifically, it assessed whether epistemic curiosity plays a mediating role in the nexus of L2 motivation, epistemic curiosity, and epistemic boredom. Data were collected from adolescent learners of English in China (N = 312). The findings from the correlation analysis indicated that epistemic boredom had statistically significant negative relationships with epistemic curiosity and L2 motivation, except for the ought-to L2 self variable, where the relationship was not statistically significant. Conversely, epistemic curiosity had a positive and statistically significant relationship with L2 motivation, except for the ought-to L2 self variable, where the relationship was not statistically significant. Next, the path analysis examined the influence of L2 motivation on epistemic boredom without considering the mediating effect of epistemic curiosity. Its findings indicated that epistemic boredom had a statistically significant negative relationship with the general motivation/attitude and general motivation/effort variables. The subsequent path analysis, which focused solely on two goal-oriented L2 motivation constructs from the Gardnerian framework, detected the mediating role of epistemic curiosity. Some pedagogical implications are drawn from these findings.