A reagent kit EIA-OCHRATOXIN A for the determination of mycotoxin ochratoxin A in feeds and foods by a direct competitive enzyme immunoassay using microtitration plate has been developed and tested. The conjugate of ochratoxin A with horseradish peroxidase was synthesized using the mycotoxin aminoderivative joined to the carbohydrate chain of the enzyme. A monoclonal antibody to the mycotoxin was immobilized on the surface of plate wells through sheep anti-mouse antibodies. The evaluated parameters of the kit and metrological characteristics of the technique of measurements correspond to the modern level of immunoassay development and provide the determination of ochratoxin A content of agricultural products in a range of 5 to 375 mg/kg with proper accuracy and precision. The limit of quantitative determination of ochratoxin A in grain and cereal foods does not exceed 5 mg/kg.