Processes of nonradiative excitation energy transfer and excited states quenching in electrochemiluminescent sensor with working electrode, modified by Langmuir-Blodgett film with incorporated electrochemiluminescer molecules, are investigated by means of mathematical modeling. Comparison with experimental results revealed that considered model is applicable for Langmuir-Blodgett films thinner than 10 monolayers. The optimal thickness of the film for electrochemiluminescent sensor operation was estimated as 3-5 monolayers.