Although previous research has documented significant and substantial relations between reading motivation and reading comprehension for late elementary and secondary school students, there is a lack of studies involving students in the early elementary grades and applying longitudinal designs. Accordingly, we conducted a longitudinal study with 1051 second- and third-grade students and measured their reading motivation and reading comprehension performance at two different time points one year apart. The results confirmed reciprocal relations between involvement (a component of intrinsic reading motivation) and reading comprehension at the word and sentence levels but not at the passage level. Competition-oriented reading motivation (a component of extrinsic reading motivation) did not predict reading comprehension but was itself negatively affected by reading comprehension. In sum, the findings suggest that even at early stages of learning to read, intrinsic reading motivation contributes to students' development of reading competence. •Reading motivation and comprehension were examined in a longitudinal study.•The subjects were elementary school students in grades two and three.•The results showed reciprocal relations between motivation and comprehension.•Only intrinsic but not extrinsic reading motivation had a significant effect.