The paper presents an algebraic characterization of observability and span-reachability of bilinear hybrid systems without guards, i.e. hybrid systems whose continuous dynamics are determined by bilinear control systems, and whose discrete transitions are triggered externally. The proposed characterization provides necessary and sufficient conditions for observability and span-reachability in terms of rank conditions for generalized observability and controllability matrices. This characterization is useful for the system theory of bilinear hybrid systems, in particular, it is used in the realization theory of bilinear hybrid systems, (Petreczky, 2006). (C) 2010 Elsevier Ltd. All rights reserved.