Buying firms involve suppliers in the new product development process to improve product development costs, lead times, and manufacturing capabilities. However, for a new product development project to be successfully executed, suppliers must clearly understand their expected tasks and responsibilities from the buying firms. Yet suppliers sometimes experience difficulties due to insufficient information and unclear specifications, as well as problems arising from interpreting certain situations differently from the buying firm's intentions. In this paper, the uncertain situations arising from such insufficient information, unclear definitions, disagreements in interpretation, and a series of misunderstandings that occur in carrying out assigned tasks are defined as the concept of project ambiguity. While such project ambiguity occurs on both the buying firm and supplier sides, this paper focused the research on the supplier side. Therefore, the subject of this study is to identify the antecedents of project ambiguity as perceived by suppliers and to examine the impact of project ambiguity on supplier project performance. Examining this phenomenon from a knowledge-based view, the study proposed product innovativeness, the buying firm's propensity to protect core knowledge, supplier absorptive capacity, and the level of buyer-supplier communication as antecedents of project ambiguity. To test the research hypotheses, a total of 103 samples were obtained from the automotive, electronics, and defense industries in Korea and analyzed. The empirical analysis results showed that product innovativeness and the buying firm's propensity to protect core knowledge had a significant impact on the project ambiguity perceived by suppliers, and that greater project ambiguity had a negative impact on performance.