The goal of the present study was to investigate the mediating effects of reading amount and metacognitive knowledge of strategy use in the relationship between intrinsic motivation and reading comprehension among secondary school students. We hypothesized that reading amount and metacognitive knowledge of strategy use in Grade 6 will mediate the relationship between intrinsic motivation in Grade 5 and reading comprehension in Grade 7 while taking into account the reciprocal relationship between intrinsic motivation and reading comprehension in Grades 5 and 7. Within the framework of the German National Educational Panel Study, 3,829 secondary school students were included in the analyses. Based on the analyses of structural equation models, we found significant indirect effects of intrinsic motivation on reading comprehension through reading amount and metacognitive knowledge of strategy use. The results of exploratory analyses on moderating effects of sex and the levels of reading skills are also discussed.