In the present study, we newly developed a kanji writing subtest of ATLAN (Adaptive Tests for Language Abilities), which is based on item response theory (Takahashi & Nakamura, 2009; Takahashi, Otomo, & Nakamura, 2012) and can be administered via the Internet. In Study 1, we evaluated two parameters, difficulty and discrimination, of 244 kanji characters based on the results of 1,306 children from 2nd to 9th grade. In Study 2, we analyzed kanji reading and writing subtests of 283 children from 3rd to 6th grade, including their error patterns and stroke order while writing kanji. The results of hierarchical regression analysis showed that more than 60% of the variance of kanji writing is explained by grade, kanji reading, and accuracy of forms and stroke order while writing kanji. The practical significance of the test is discussed.