Motivation is vital to student learning. Previous research suggests that interactive digital textbooks may enhance students’ motivation in mathematics education. Nevertheless, this claim is not based on motivation theory. According to self-determination theory, the basic psychological needs of autonomy, competence and relatedness must be fulfilled to achieve intrinsic motivation. The present investigation utilizes a 17-item questionnaire to assess high school students’ sense of basic psychological needs when using interactive digital textbooks in mathematics. Moreover, the study investigates the relationship between these needs and emotional engagement, which reflects enjoyment and interest. Among the 74 students invited to participate, 63 returned the questionnaire. The results indicate that students’ senses of autonomy and relatedness were relatively high when using the e-book, whereas the sense of competence was low to moderate. Most notably, the e-book’s reward system only provided a moderate sense of progress. Emotional engagement correlated with autonomy (r=0.71, p<0.001), relatedness (r=0.63, p<0.001) and weakly to competence (r=0.39, p=0.003). The e-book’s reward system did not contribute to the weak association between competence to emotional engagement. The study provides new insights on interactive digital textbooks and motivation, that are based on motivation theory. However, the present sample is small, limiting the result’s generalizability. Larger studies are therefore encouraged to validate and further expand on the results.