The objective in this paper is to introduce a new methodology for strategic module sharing in service family design using game theory to model situations involving uncertain market environments. We extend concepts from platform-based product family design to develop a methodology for module-based service family design. A module selection problem is considered as a strategic game with incomplete information that is described by services' market share ratios and customer's preferences. We employ a Bayesian game to model uncertainty situations regarding market environments and determine strategic equilibrium solutions for selecting modules for the service family being designed. To demonstrate implementation of the proposed Bayesian game, we use a case study involving a family of banking services.