In Japan, the steel‐concrete composite girder bridge is widely used to reduce construction and maintenance cost, and improve constructability and the construction period. As an effort to decrease box girder construction cost, the narrow box girder bridge, which has a reduced box girder width, has been developed. Compared with a conventional box girder bridge, this type of box girder bridge simplifies the structure inside the box by narrowing the space between web plates. Furthermore, it is possible to reduce the number of members, welding length and painting area. The average economical span length is approximately 90m. Similarly, in European countries, a new type of composite girder bridge was developed and constructed for the same purpose as the bridge in Japan. The steel‐concrete double composite girder bridge, which has two concrete slabs on the upper and lower surfaces of the girder only in the region of the intermediate supports, is a type of medium span bridge. An advantage of adopting this structural system is that the cross sections of both the sagging and hogging bending moment areas are classified into the compact section at the ultimate limit state; that is, the maximum flexural strength of these sections can be taken full plastic moment. There are few constructed examples of this type of bridge in Japan. Because of the handling difficulty, the shop manufacturing cost of a box girder is, generally, more expensive than that of an I‐girder. Additionally, the design method for bridges has been revised since January 2018 and has changed from the allowable stress design method to the limit state design method in Japan. Therefore, the authors propose a new type of steel‐concrete double composite I‐girder bridge. The trial design of three‐span continuous girder bridges was conducted. In this paper, the effect of double composite action, for instance, the reduction of the girder height in the region of the intermediate supports, and applicable span length are discussed.