Aromatase (CYP19) is a rate-limiting enzyme that catalyzes the biosynthesis of estrogens. Imaging agents based on aromatase inhibitors (AIs) have been developed for a PET/SPECT study. A series of compounds was synthesized based on YM511, which has previously been used for breast cancer treatment. Two examples of these derivatives, 4-(((4-iodophenyl)methyl)-4H-1,2,4-triazol-4-yl-amino)-benzonitrile (5) and 4-((1H-imidazol-1-yl)(4-iodobenzyl)amino)benzonitrile (11), displayed potent binding affinities to human aromatase (IC50 = 0.17 and 0.04 nM, respectively). Biodistribution and autoradiographic studies revealed that [125I]5 and [125I]11 were highly accumulated in the stomach (16.21 and 10.88% dose/g, respectively) and ovaries (8.56 and 3.32% dose/g, respectively) of female rats. Log P of [125I]5 was 2.49, meaning good brain penetration. Autoradiograms of brain sections showed a high uptake in the bed nucleus of the stria terminalis and amygdala. These results suggest that [125I]5 and [125I]11 are potent probes for aromatase imaging in both the brain and peripheral organs.