This article reports the results of a study that assesses the effectiveness of a Philosophy in Schools (PIS) program in developing English as a Second Language (ESL) students' thinking skills and English competence in Hong Kong. In the study, training and support were provided for two English teachers to enable them to teach PIS to their Secondary 4 ESL students during English lessons. The students were found to be capable of reasoning and arguing about philosophical problems arising from various stimuli prepared by their teachers according to the English curriculum. Also, PIS was found to play an important role in promoting the students' critical and creative thinking and enhance the development of their English language proficiency to a significant extent. The findings of this study suggest that integrating philosophy into the English curriculum can promote critical thinking, creative thinking, and English language proficiency in ESL students.