An experiment was designed to investigate the effects of translation and performance on memory of words of Sign Language as a second language. An intermediate class of Sign Language learners, whose first language was Japanese, was required to carried out four tasks : translating from Japanese word into Sign Language word, oral reading of Japanese word, translating from Sign Language word into Japanese word, and performing (expressing) of Sign Language word. The subjects were then asked unexpectedly to free recall words in Japanese they had learned. The results showed that item recalls for translating conditions were better than those for oral reading condition and performing condition. These effects were discussed based on the bilingual dual coding theory which assumes the independent and interconnected storage systems for word memory of first language and second language. From the viewpoint of Linguistics, Sign Language is able to be regarded not as a speech language but as a visual language. The results indicated that Sign Language was not visual imagery but a "natural language" in spite of that linguistic feature. It was educationally suggested that both meaning presentations in first language and imagery instruction are quite important by vocabulary learning of Sign Language.