Utilizing multiple small-sized automated guided vehicles (AGVs) in cooperatively transport large and heavy objects in manufacturing factories or logistics is an emerging research direction. Flexibility and efficiency can be enhanced by using multi-AGV comparing to a large AGV with higher capacity especially in clutter environments. In this paper, a multi-AGV system by using Mecanum wheels to provide omnidirectional movement is proposed for cooperative transportation. Accordingly, the proposed Mecanum-wheeled automated guided vehicles (MWAGVs) composed of Mecanum wheels and a rotary platform provides not only non-constrained movement but also planar displacement for allowance of distance errors. In the proposed MWAGVs, the formation control with fixed geometry during operation is significant especially with unknown object information, dynamic uncertainties, and external disturbances. Therefore, the passivity-based adaptive synchronizing control algorithm is developed to ensure stability and tracking performance with uncertain dynamic parameters. Simulations and Experiments show the efficacy of designed Mecanum-wheeled AGV.