The study aimed to assess the aldose reductase (AR) inhibition of selected Geranium species and determine the bioactive flavonoid constituents. Flavonoids are known to be good AR inhibitors. Among the species examined, G. sibiricum exhibited potent inhibition of AR (IC50 value, 2.4 µg/mL). Further examination of G. sibiricum, after solvent extraction and fractionation, revealed that the ethyl acetate fraction (IC50 value, 0.41 µg/mL) had a potent AR inhibitory effect. Kaempferol rhamnosides were the active compounds from this fraction. Moreover, G. sibiricum showed the highest content of kaempferol-7-O-rhamnoside and kaempferol-3,7-O-dirhamnoside among the samples examined with a concentration in the extracts of 28.1 and 2.2 mg/g, respectively. This study shows that G. sibiricum exhibits promising AR inhibitory activity, which can be explored further as a natural therapy for treating and managing complications associated with diabetes.