Extensive studies on the effect of a low intensity magnetic field on microbial activity have been reported. However, they are often controversial; the magentic fields are accelerative on the growth, or inhibitory, or noneffective. The inconsistency of the results is mainly because the experimental conditions were improperly controlled and well characterized microbial strains were not used. Following the invention of superconductive materials, high magnetic fields produced by superconductive magnets will be applicable to various microbial reaction control. In this paper, a super high magetic field of 11. 7 tesla (T) was imposed on the auxotrophic bacteria of Escherichia coli and the effect of the magnetic field was investigated under various nutritional and temperature conditions. The 11. 7 T was also imposed on E. coli where the bacteriophage lambda was lysogenic and carries a temperature-sensitive mutation in the phage repressor gene. The transition from lysogenic to lytic process was investigated. A new bioreactor which was operated under 7 T superconductive magnetic field was introduced.