The purpose of this study is to investigate in-depth high school students’ strategy use in reading English texts of College Scholastic Ability Test (KSAT). This study employed a think-aloud method to look into the reading process by task types and by reading proficiency. Six high school students, three high-level and three low-level readers, were asked to perform reading tasks of three types, ‘finding a theme’, ‘filling the gap’, ‘finding an irrelevant sentence & inserting a sentence’, thinking out loud after training. The results are as follows. First, the participants used varied types of reading strategies regardless of top-down/bottom-up. ‘Guessing from the context’ and ‘paraphrasing in L1’, were most frequently used, and ‘using schema’ and ‘sensing the logical organization’ were least used.’ Second, different strategy use patterns were shown by task types: Far more strategies were used in ‘finding a theme’ than the others, especially, attending to keyword. Third, the high-level readers employed more reading strategies than the low-level counterparts. Furthermore, the strategy use pattern was very different between groups: The low-level readers seldom used ‘checking discourse markers,’ ‘synthesizing information,’ and ‘questioning’ that the high level readers commonly used.