To cite this version:Abstract: This paper deals with the state and input observability analysis for structured bilinear systems with unknown inputs. More precisely, we provide two groups of conditions, the first ones are necessary and the second ones are sufficient, to check whether or not a structured bilinear system generically state and input observable. These conditions, which are far to be trivial, are expressed in quite simple graphicterms. Moreover,the proposed method assumes only the knowledge of the system's structure and all the given conditions are easy to check because they deal with finding paths in a digraph. This makes the suggested approach particularly well suited to study large scale systems or systems with unknown parameters, as it may be the case during a conception stage.