Flavonoids, which have many biological activities and have been widely used in nature, can be artificially synthesized. However, regioselective cyclization of chalcones is difficult by chemical methods. In this study, we demonstrated that Aspergillus niger is capable of cyclizing chalcones to flavanones, affording a mimic of plant biosynthetic processes. Chalcones 1-6 were biotransformated to the modified chalcones 8-14 and to the flavanones 15-27. The biotransformation showed that enzymatic cyclization and demethylation occurred during the first days of biotransformation; in contrast, hydroxylation is a later process. With a longer culturing time, it is possible to obtain more hydroxylated flavanones with excellent yields.