Production and manufacturing systems often involve a myriad of interrelated activities. How these activities are organised and scheduled has a significant effect on the success of a system. Recently, the Design Structure Matrix (DSM) has been regarded as an effective tool for modelling and scheduling interrelated activities. Based on fuzzy set theory, this study explicitly addresses the uncertain activity dependencies in our formulation and develops a mathematical model for sequencing interrelated activities in a DSM. Because of the complexity of the model, a new approach, which embeds an exact algorithm within a framework of a local search heuristic, is presented for solving large problem instances. Testing results demonstrate that relatively good solutions can be easily obtained by our approach, thereby providing managers with an effective tool for scheduling a large number of interrelated activities with uncertain dependencies.