A high-stake standardized test (e.g., TOEFL, TOEIC, and IELTS) is one of essential indicators in determining students’ English proficiency especially in the context of English as a Second Language (ESL) and English as a Foreign Language (EFL). Direct test preparation method is prevalent in test preparation course; however, negative washback could occur. Communicative Language Teaching (CLT) can be effective teaching method which can diminish the negative washback and also increase both proficiency and test score. The purposes of this study were 1) to examine the effect of CLT on students’ TOEIC score and 2) to explore students’ attitude towards the use CLT in test preparation course. The sample was 68 Business English students selected by purposive sampling divided into experimental group and control group. The instruments were pre-test, the official TOEIC score and semi-structured interview. The data were analysed by using mean, standard deviation, t-test and content analysis. The results revealed that the official TOEIC score of the experimental group was significantly higher than the control group which indicated that CLT in test preparation course yielded a positive effect on improving students’ TOEIC score.