In spite of high piezoelectricity, only a few one-dimensional ferroelectric nano-materials with perovskite structure have been used for piezoelectric nanogenerator applications. In this paper, we report high output electrical signals, ie an open-circuit voltage of 3.2 V and a closed-circuit current of 67.5 nA (current density 9.3 nA cm− 2) at 0.38% strain and 15.2% s− 1 strain rate, using randomly aligned lead-free KNbO 3 ferroelectric nanorods (∼ 1 μm length) with piezoelectric coefficient (d 33∼ 55 pm V− 1). A flexible piezoelectric nanogenerator is mainly composed of KNbO 3–poly (dimethylsiloxane)(PDMS) composite sandwiched by Au/Cr-coated polymer substrates. We deposit a thin poly (methyl methacrylate)(PMMA) layer between the KNbO 3–PDMS composite and the Au/Cr electrode to completely prevent dielectric breakdown during electrical poling and to significantly reduce leakage current during excessive straining. The flexible KNbO 3–PDMS composite device shows a nearly frequency-independent dielectric constant (∼ 3.2) and low dielectric loss (< 0.006) for the frequency range of 10 2–10 5 Hz. These results imply that short and randomly aligned ferroelectric nanorods can be used for a flexible high output nanogenerator as well as high-k capacitor applications by performing electrical poling and further optimizing the device structure.