Larval anuran jaw sheaths are corneous flat covers overlying the lateral surface of upper and lower jaws. Although most anuran tadpoles have a single sheath on both jaws, some have a pair of divided sheaths on one or both jaws, and sometimes both undivided and divided conditions are observed even within a species. We examined morphology of larval specimens tentatively identified as Meristogenys amoropalamus, collected from Borneo, and found that the lower jaw sheaths changed from a divided to an undivided state with larval development. Furthermore, the numbers of undivided rows of lower labial tooth, and of serrations of upper and lower jaw sheaths also changed ontogenetically. From these observations, we suggest that developmental stages should be taken into consideration when we use these larval characters for morphological comparisons in this genus.