In this research, the evaluation of in vitro serine protease inhibitory activity of ten plant species was aimed, and extracts that showed strong activity were analyzed through HPLC. Rhododendron caucasicum Pall. (leaf) and Potentilla reptans L. were found to have the highest chymotrypsin inhibitory activities (83.77 and 82.01% inhibition). While the highest trypsin inhibitory activity was observed in R. caucasicum (flower) (%82.86 inhibition), followed by Cruciata laevipes Opiz (82.22% inhibition). Extracts showing strong enzyme inhibition were fractioned and subjected to activity tests. The highest chymotrypsin inhibitory activity was observed in the n‐hexane fraction of P. reptans (92.90% inhibition), while the highest trypsin inhibitory activity was found in the ethyl acetate fraction of Lythrum salicaria L. (89.81% inhibition). HPLC studies determined that the 80% ethanol extract of P. reptans contained chlorogenic acid. The screened plants were generally rich in phenol and flavonoid content and showed strong antioxidant activity.