Single phase and highly crystalline biocompatible ferroelectric (Na,K)NbO3 (NKN) nanofibers were synthesized by sol-gel assisted electrospinning technique. Low amplitude piezoelectric response as well as electrostriction effect in NKN fibers were examined using piezoelectric force microscopy technique. Piezoelectric coefficient d(33) is strongly anisotropic varying from 75.8 to 18.3 pm/V for, respectively, out-of-axis and on-axis oriented ferroelectric domains in NKN fibers. Hysteresis P-E loop for individual nanofiber reconstructed from the bipolar E-field-induced butterfly strain curve yields: coercive field E-c = 31 kV/cm, remnant P-r = 6.2 mu C/cm(2), and the maximum achieved polarization P-max = 21.2 mu C/cm(2). Enhanced piezoelectric effect and strong electrostriction promise NKN fibers as electrically polarizable scaffolds for tissue engineering and for energy harvesting biocompatible nanogenerators. (C) 2014 AIP Publishing LLC.