The objective of this study was to investigate developmental changes of processing speed of two different scripts, i. e., kana and kanji in elementary school years. In experiment 1, second and sixth grade children, and adults performed Stroop task, in which color words written in kana and kanji scripts were used as disturbing stimuli. Interference in kana script was bigger than in kanji for second grade children, but it showed about the same amount of interference between kana and kanji in the other two groups. In experiment 2, fourth grade children performed Stroop task, but this time, they were divided into two subgroups according to their knowledge of kanji letters. The result of good kanji group was similar to that of the sixth grades in exp. 1, although the poor kanji group showed similar performance as the second grades. These results showed that semantic processing speed of kanji would catch up with kana through elementary school years. Finally, the relationship between the semantic processing of kana and kanji in Stroop task and processing speed while reading sentences written by them was discussed.