Inference of unknown words for ESL/EFL learners is considered to hold a primary position in research fields. Many research studies have shown that the inference of unknown words as well as the context method to be important. However, the results of the studies have not always been consistent. Therefore, the most frequently used inference clues for Japanese EFL high school students were investigated in this study. As a result, out of all 10 items among the correct inference group, was the clue 2. the sentence that includes the target word. According to the frequency order, the clue 1. one or two words before or after the targetword, and the clue 3. a specific part of the passage except the sentence that includes the target word were listed. These 3 inference clues were classified as Contextual Clues based on the classification of Aizawa (1998b) which modified Haastrup's (1987). From this result, it was clearly found that Japanese EFL high school students could use local contextual clues without being taught. This suggests that if the training for inferring unknown words and strategy instructions were done along with teaching vocabulary and reading, then more effective use of context, (which includes global context), would be expected.
