Lead-free (K, Na)NbO3 single crystalline nanorods (KNN NRs) with environmental compatibility and a high piezoelectric coefficient may find increasing applications including piezoelectric nanogenerators. To optimize the piezoelectric responses of KNN NRs, the K/Na ratio must be adjusted precisely to a critical value. In this work, composition-controlled KNN NRs were successfully synthesized via the molten-salt reaction, and some advanced measuring techniques, such as Raman, ICP, TEM, DSC, etc., were employed for the detailed characterization. The compositional homogeneity along the length direction of an individual NR was confirmed by confocal Raman spectroscopy. Furthermore, this work revealed the correlation between the characteristic frequencies of Raman spectra and K/Na ratio of KNN nanocrystals, which can be used as a simple and convenient method for non-destructive and quantitative analysis of the A-site composition in alkaline niobate perovskite compounds.