It has been two decades since bovine spongiform encephalopathy(BSE) was first recognized in UK. After the emergence in UK, BSE cases reported in European countries, North America, Israel and Japan. In UK, number of BSE cases turned to decline after 1993, and BSE cases are now decreasing in many European countries, suggesting the occurrence of BSE is hopefully coming to an end in near future. Although there are limitations on performing experiments such as long incubation periods and the use of cattle for pathogenetic studies, there are many research outcomes on BSE during the two decades and those are adapted for control measures for BSE. Extensive active surveillance of prion diseases in ruminants in European countries and Japan clarified the exact incidence of the diseases in ruminants, however, the surveillance also disclosed other concerns, for instance, the existence of atypical BSE cases and possibly BSE prion -infected goats in the field.