In this acoustic study, preboundary lengthening (PBL) in Japanese is investigated in relation to the prosodic structure in disyllabic words with different moraic and pitch accent distributions. Results showed gradient progressive PBL effects largely independent of the mora count. The domain of PBL is better explained by the syllable structure than the moraic structure. PBL, however, is attracted toward a non-final moraic nasal, showing some role of the mora. The initial pitch accent does not attract PBL directly, but it suppresses PBL of the final rime as a way of maintaining the relative prominence, showing a language-specific PBL modulation.