A very good application of FRP composites has been proved in case of hundreds of pedestrian bridges. However, there exists only very few of all-composite bridges that are suited for the heavy traffic load classes. The innovative idea of an all-composite girder-deck structural system for small bridges suited for the heavy traffic load classes has been proposed and experimentally tested under static and dynamic load. The all-composite bridge girder is combined with a U-shaped open box with slightly inclined webs and two top flanges and a sandwich slab bonded to the top flanges with epoxy adhesive. The composite action of both elements under service load was assumed in the design of the bridge superstructure. The top and bottom flanges of the box were made of solid GFRP composites whereas the webs were made in form of the sandwich panels with PVC foam layer in-between two GFRP laminates. The sandwich bridge deck slab consisted of two GFRP laminates and PUR foam core stiffened with the internal vertical GFRP ribs. To increase the torsional stiffness of the girder and to prevent buckling of webs, internal diaphragms were placed and bonded along the length of the girder. The most important issues in structural behavior of all-composite bridges are: girder stiffness, ultimate strength, failure mode, strength of its longitudinal adhesive joints and global safety factor. These performance characteristics of the new all-composite bridge girder have been evaluated on the basis of static load tests carried out on the full-scale model. After comprehensive laboratory testing, which had revealed expected structural performance, the girder was used in the first Polish all-composite bridge.