This study aims at (1) investigating the quality of “Buku Bahasa Inggris Untuk SMA/K” textbook to teach English for the tenth grade students of accounting skill program at SMK N 1 Randudongkal, and (2) developing English supplementary textbook for the tenth grade students of accounting skill program at SMK N 1 Randudongkal. It is a Research and Development study. There are two steps in conducting this study. The first is exploration, which consists of library research, book analysis, and need analysis. The second is model development which consists of design the draft prototype, experts judgment, try out, and final product . 
The result of book analysis reveals that “Buku Bahasa Inggris Untuk SMA/K” has some weaknesses for teaching English for accounting students. The materials in the existing textbook are still general. The teacher should find related materials from other resources. Then, the researcher analyzed the needs of students through conducting interview and delivering questionnaire to accounting students. The result showed that the students need English materials specifically for accounting. Based on the result of exploration stage, the researcher decided to design English supplementary textbook for accounting students based on inquiry-based language learning (IBLL). 
The reasons the researcher chose IBLL is that IBLL provides teaching steps which emphasize students as center of learning. Furthermore, it could engage students in teaching process and stimulates students to be more critical and creative in thinking. 
In development stage, the researcher designed draft prototype based on the result of exploration stage. Then, it is evaluated by two experts in TEFL. The researcher revised the draft prototype based on the suggestion from the experts. After it was revised, it was tried out to accounting students in order to get the feasibility of the draft prototype. At the end of the try out, the researcher conducted FGD and delivered questionnaire to know the students’ responses toward the draft prototype. The result of FGD and questionnaire were used to revise the draft prototype into the final product. 
It is hoped that the English supplementary textbook for accounting can help the teacher in teaching English for accounting students. The researcher also hopes that the students’ motivation and the situation of the classroom improve. 
Keywords: ESP, English textbook, supplementary textbook, vocational school, accounting skill-program