The improved piezoelectric immunosensors for determination of atrazine have been developed. To immobilize a biorecognition layer, the surface of a gold electrode of the piezoresonator crystal was modified by a self-assembling thiol monolayer using either cystamine, 4-aminothiophenol, or dithiobis(succinimidyl propionate). The measurements were performed in a flow-through arrangement using Electrochemical Quartz Crystal Nanobalance (EQCN). The competitive assay procedure was tested with atrazine immobilized on the surface through albumin as a bridge molecule. In the competitive assay for atrazine, the monoclonal anti-atrazine antibody D6F3 was employed. The mixture of antibody with either standard or sample was pre-incubated and then injected to the flow cell. The kinetic binding curves were recorded continuously. The non-linear fitting procedure and a calibration curve have allowed us to determine atrazine concentrations as low as 0.01 ppb, the upper limit of detection being 1 ppm. The regeneration of piezosensors has also been improved by utilizing a carboxylated atrazine derivative for immobilization and hydrolysis of immunocomplexes using proteinase. In the direct piezoelectric immunosensor for atrazine, the antibody D6F3 was immobilized covalently on the sensing surface. This immunosensor allowed us to detect directly atrazine in samples without using any labels. The regeneration procedure has also been developed.