In our efforts to solve problems associated with the treatment of garbage wastes, a novel, efficient process utilizing a small bioreactor equipped with a heating and an agitating apparatus was developed. The use of this process, which reduces and stabilizes garbage wastes, can be distinguished from other similar treatment processes that utilize similar equipment by its highly stable operation. This advantage led us to consider a characteristic microflora that would play an important role in the process. Thus, we analyzed the structure of the microflora in the process using molecular biological methods. The major microorganisms inhabiting the treatment environment were usually maintained for several weeks although garbage waste was added to the system each weekday. Moreover, surprisingly, lactic acid bacteria constituted a large majority in the microflorae in spite of the thermoacidophilic conditions in the reactor. These analyses permitted a better understanding of the mechanism of the process, especially of its stability.