The effects of word frequency were examined for Japanese Kanji and Katakana words in 6 experiments. The sizes of frequency effects were comparable for Kanji and Katakana words in the standard lexical decision task. In the standard naming task, the frequency effect for Katakana words was significantly smaller than that for Kanji words. These results were consistent with the lexical-selection account of frequency effects offered by dual-route models. Contrary to this account, however, frequency effects were smaller for Katakana words than for Kanji words in go/no-go naming tasks, in which participants were asked to name a stimulus aloud only if it was a word. This Frequency × Script Type interaction was not the result of using a go/no-go task because the interaction disappeared in the go/no-go lexical decision task. These results pose a strong challenge for the lexical-selection account of frequency effects offered by dual-route models.