The present study represents an attempt at investigating the relationship between the Japanese Sign Language proficiency and the Japanese literacy skills of high school students who are deaf and hard-of-hearing (D/HH). A pilot test of Japanese Sign Language was designed and administered to 138 D/HH students. A validation analysis was carried out employing classical test theory methods, and test scores were compared to scores obtained by the same participants on a Japanese language and literacy test. Although the small number and heterogeneity of the items in the Japanese Sign Language Test lowered the test's reliability estimate, the comparison with the Japanese language and literacy test provided useful insights into the relationship between the two languages. In particular, students who performed well on the general narrative comprehension task of the Japanese Sign Language Test, and those who were good at processing sequential information in Japanese Sign Language, also had good overall command of written Japanese. Moreover, there seemed to be a positive correlation between students' metalinguistic awareness of Japanese Sign Language and their knowledge of Japanese grammar.