The aim of this paper is to pursue the factors contributing to high school students' speaking proficiency. In this paper, the data obtained were computed and the multiple regression analysis was conducted with the results of two types of speaking tests : the "picturecued test" and the "topic-based test" were the dependent variables, and the other tests plus eight metacognitive factors were the independent variables. The result showed that the common factor contributing to speaking proficiency was comprehensive English ability. On the other hand, the diverse factors between the two were grammatical ability (topic-based test) and trying to focus on the content to convey meaning and obstructive factors of speaking : (1) linguistic processing strategy.