We present piezoresponse force microscopy measurements on individual integrated potassium niobate (KNbO3) nanowires. The devices consist of KNbO3 nanowires on SiO2 substrates being mechanically clamped and electrically biased by lithographically defined metal electrodes. This configuration allows to apply electrical fields parallel to the nanowire axis. Measured piezoelectric displacements reveal a multidomain structure of the nanowire. We observed displacements in the range of 3-13 pm on different domains under V-ac of 2 V, that have typical section length of approximate to 200 nm, along a doubly clamped nanowire with approximate to 100 nm diameter. A maximum nominal piezoelectric coefficient of 7.9 pm/V has been extracted.