Benzylisoquinoline alkaloids such as morphine, which are naturally produced by plants, have high physiological activity and are used as pharmaceutical raw materials, cosmetics, and functional ingredients. However, most benzylisoquinoline alkaloids are present only in small amounts in plants, and their production by extraction from raw materials is relatively expensive. Thus, the creation of efficient production systems is desirable. In recent years, comprehensive genetic analyses have revealed the biosynthesis pathways of benzylisoquinoline alkaloids in various plants, including poppy. Fermentative production of useful plant components in microorganisms by applying synthetic biology techniques has attracted much attention. Application of these approaches has made it possible to produce plant alkaloids at a practical level by microbial fermentation. This chapter outlines the status, challenges, and future prospects of the production of benzylisoquinoline alkaloids by microbial fermentation, particularly morphinan alkaloids, which are important pharmaceutical raw materials.