The discovery of selective inhibitors for acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) is extremely important for the development of drugs that can be used in the treatment of patients diagnosed with the Alzheimer's disease (AD). For this reason, there is a growing interest in developing rapid and effective assays techniques for cholinesterases (ChE) enzymes ligand screening. Herein is presented the results of selective screening assays of a coumarin derivatives library using BChE and AChE covalently immobilized onto silica fused capillaries (ICERs, 15cm×0.1mm ID). The statistical comparison of the ICERs screening assay with that of the free enzymes is reported and highlights the advantages of the on-flow ICERs assay. Two out of 20 coumarin derivatives could be highlighted: compound 17 is more active toward BChE (IC50=109±21μM) and 19 showed activity against both enzymes (BChE IC50=128±28μM and hu-AChE IC50=144±40μM). The statistical evaluation of the results of the ICERs and free enzyme assays showed no difference between them, further validating the ICERs assay model. The ICERs ability to recognize selective ligands and its use for characterization of the inhibition mechanisms of the hits consolidates the approach here reported.