The present disclosure relates to a sensor network, machine type communication (MTC), machine-to-machine (M2M) communication, and technology for Internet of things (IoT). The present disclosure may be applied to intelligent services based on the above technologies, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method and an authenticating system for authenticating users in an IoT environment are provided. The method includes receiving an access request to at least one device present in the IoT environment, identifying a type of questions based on at least one of a user interface (UI) type of the at least one device, or an authentication level of the at least one device, generating at least one question corresponding to the type of questions based on at least one of user data of a user associated with the access request, or device data of one or more devices associated with the user, presenting the at least one question to at least one of the user and the one or more devices, and authenticating the user to access the at least one device based on a response for the at least one question received from the at least one of the user and the one or more devices.