English words with an inconsistent grapheme-to-phoneme conversion or with more than one pronunciation ("homographic heterophones"; e.g., "lead"-/lεd/, /lid/) are read aloud more slowly than matched controls, presumably due to competition processes. In Japanese kanji, the majority of the characters have multiple readings for the same orthographic unit: the native Japanese reading (KUN) and the derived Chinese reading (ON). This leads to the question of whether reading these characters also shows processing costs. Studies examining this issue have provided mixed evidence. The current study addressed the question of whether processing of these kanji characters leads to the simultaneous activation of their KUN and ON reading, This was measured in a direct way in a masked priming paradigm. In addition, we assessed whether the relative frequencies of the KUN and ON pronunciations ("dominance ratio", measured in compound words) affect the amount of priming. The results of two experiments showed that: (a) a single kanji, presented as a masked prime, facilitates the reading of the (katakana transcriptions of) their KUN and ON pronunciations; however, (b) this was most consistently found when the dominance ratio was around 50% (no strong dominance towards either pronunciation) and when the dominance was towards the ON reading (high-ON group). When the dominance was towards the KUN reading (high-KUN group), no significant priming for the ON reading was observed. Implications for models of kanji processing are discussed.