The purpose of this study is to clarify the degree of comprehension of 19 signs (Tokuda, 2003) and the “reading" of these signs from the perspective of children with mentally challenged. Among the 19 signs as question items, 4 were signs of symbols and 15 were signs of pictures. This study measured the degree of comprehension of the signs with 18 junior high school students and 22 high school students with mental disorders . The results of the investigation are presented as follows . The children with mentally challenged were able to comprehend the sign. They were also able to follow the movement from the picture of the sign. Therefore, it can be stated that if the children studied the signs, they were able to understand it. Moreover, this study confirmed that children with mentally challenged faced the following problems while reading the signs: 1) The degree of comprehension of the sign of the symbols was observed to be low. 2) They made several mistakes while reading the signs of the pictures . 3) The children did not understand the rules pertaining to the signs. 4) They found it difficult to apply the understanding of the rule of one sign to that of another sign. Therefore, children with mental retardation require a more comprehensive studying of these signs in order to understand them.