Aromatase, a cytochrome P450 hemoprotein that is responsible for estrogen biosynthesis by conversion of androgens into estrogens, has been an attractive target in the treatment of hormone-dependent breast cancer. As a result, a number of synthetic steroidal or nonsteroidal aromatase inhibitors have been successfully developed. In addition, there are several classes of natural products that exert potent activities in aromatase inhibition, with the flavonoids being most prominent. Previous studies have exploited flavone and flavanone scaffolds for the development of new aromatase inhibitors. In this paper, we describe the design, synthesis, and biological evaluation of a novel series of 2-(4'-pyridylmethyl)thioisoflavones as the first example of synthetic isoflavone-based aromatase inhibitors.