The TOEIC has widely used to evaluate business English proficiency in Korea, but those who achieved high scores still often face difficulties in performing their duties in English at work. This implies that the test may not evaluate business English proficiency effectively enough. With an ultimate goal of proposing an effective way of assessing business English proficiency, therefore, his study analyzed the predictive validity of the TOEIC. A correlation analysis was conducted between TOEIC scores of 64 office workers of multinational companies and their working skills in English evaluated by themselves, and their colleagues and seniors. Its results illustrated a significant correlation between their listening and reading scores and their working skills measured by all the groups, but not between their scores and their working skills in speaking and writing. In addition, the study did a delphi study to identify working skills in English to be assessed in business English tests and a contents analysis of the TOEIC. The results suggest business English tests should be able to assess working skills by work types and more direct testing of working skills in speaking and writing is needed.