This paper explores empirical factors that explain the English proficiency of senior high school students studying English at a high school in Hiroshima Prefecture, Japan. Two studies are reported. Study 1 comprised a factor analysis and a multiple regression analysis, addressing students' reading strategy. A factor analysis revealed 9 factors : (1) understanding of main points, (2) ample input/output, (3) focus on key information, (4) reading with questions in mind, (5) top-down strategy, (6) bottom-up strategy, (7) confidence in Japanese reading ability, (8) word-by-word reading and (9) basic study. A multiple regression analysis revealed three factors to explain reading comprehension ability. These factors were : (1) understanding of main points, (2) reading with questions in mind, and (3) top-down strategy. Study 2 comprised a multiple regression analysis, exploring factors to explain the students' comprehensive English ability. This study afforded an explanation by three factors : (1) English lexico-syntactic ability, (2) modern Japanese ability and (3) motivational intensity.