The information available to the system is incomplete in many applications like Decision Support Systems, Control Systems and Medical Expert Systems. Sometimes decision has to be taken under risk with incomplete information. Fuzzy logic deals with incomplete information with belief rather than likelihood (probability). The fuzzy set is defined with single membership function. The fuzzy set with two membership functions will give more information than single membership function. In this paper, the Fuzzy Certainty Factor (FCF) is studied as difference between fuzzy membership functions "true" and "false" for decision making. The fuzzy certainty factor is studied for fuzzy risk set. The fuzzy inference is studied. Business application is given as an application to fuzzy risk set.