The study attempts to examine the antecedents and consequences of the job-enlargement of the planning staff in the media agencies and to discuss how managers and the staff can respond to the trend of the job-enlargement. The research interviewed seven managers working in the media agencies and three managers from the advertising agencies. In the second stage, questionnaires were distributed in the four relevant industries: the advertiser, the media, the media agency, and the advertising agency, and 89 staff members answered the questionnaire. The results show that job-enlargement of the planning staff in the media agencies is becoming the trend. The tasks of the planning staff primarily focus on services related to the media industry, and are further required to provide trend information about various industry environments and analyses of consumer behaviors. The job-enlargement of the planning staff in the media agencies primarily results from the advertiser's requirements and the plural development of the media. The relationships between the media agency and the advertising agency are changing from vertical channel partners to horizontal competitors. The advertisers benefit the most from the job-enlargement and are satisfied with the performance of the planning staff. The media agencies may provide more training, rotation opportunities, support and assistance for the planning staff. The planning staff needs to identify their weakness and improve it by active learning, and also to cultivate open-minded and positive attitudes toward their jobs.