Doxycycline has a wide range of antimicrobial and anti-infl ammatory properties and is used to treat various infectious diseases. Spectroscopic, chromatographic, electrochemical, immunoassay and other methods are used to determine tetracycline antibiotics in various objects. Planar sensors allow express detection of antibiotics in small sample volumes. Planar potentiometric sensors based on ion associations doxycycline – tetraphenylborate (Copt = 2–3%), modifi er – polyaniline, for the quantitative determination of doxycycline have been developed. It has been found that for non-modifi cated sensors, the linearity intervals of electrode functions are 1×10 -4 – 5×10 -3 M, Cmin – 5,0×10-5 M, angular coeffi cients – 50±2 mV/pC, response time – 25 s. It is shown that the introduction of a modifi er into the carbon-containing ink of sensors leads to the stabilization of their potential, to an increase in the angular coeffi cients of electrode functions (56±1), reduced response time (20 s) and reduced detection limit (4.0 ×10-5 M). It is shown that the introduction of the modifi er into the carbon-containing ink of the sensors leads to stabilization of their potential, to an increase in the angular coeffi cients of electrode functions (56±1), a decrease in response time (20 seconds) and a decrease in the detection limit (4.0 ×10-5 M). Doxycycline sensitive sensors have selectivity to the base ion (Ki/j < < 1) and inorganic cations (Ki/j (K+) = 0.61; Ki/j (Na+) = 0,01; Ki/j (Mg 2+) = 0,01; Ki/j (Ca2+) = 0.09), and indicate the possibility of determining doxycycline in human biological fl uids. Against the background of oral liquid, the angular coeffi cients of electrode functions (45±1 mV/pS) decrease, which is associated with the background infl uence of oral liquid. The developed planar sensors are used to determination doxycycline in medicinal and biological media.