some information about an underlying system, might be imprecise represented in the form of fuzzy numbers. Thus, it is necessary to generalize The Bayesian system reliability assessment and the Bayesian estimation on lifetime data under fuzzy environments are studied in this thesis. In order to apply the Bayesian approach, the fuzzy parameters are assumed as fuzzy random variables with fuzzy prior distributions. The (conventional) Bayesian estimation method will be used to create the fuzzy Bayes point estimator of system reliability and lifetime data by invoking the well-known theorem called Resolution Identity in fuzzy sets theory. Also, Bayesian system reliability assessment under vague environment is investigated.
