We prepared (K 0.5 Na 0.5 )NbO 3 (KNN) ceramics with the addition of 1mass% ZrO 2 with the aim to hinder the exaggerated grain growth encountered in KNN. Both KNN and KNN-ZrO 2 ceramics sintered at 1115°C and 1125°C, respectively, had relative density exceeding 95%. KNN had a bimodal microstructure, with a population of fine grains of a few 100nm and the large grains of about 20μm, while the microstructure of KNN-ZrO 2 was fine and uniform, with the median grain size of 0.3μm and the largest grains of about 1.3μm. We attribute the refinement of the microstructure to the matrix grain-growth inhibition by ZrO 2 addition. The influence of ZrO 2 is twofold: sub-100nm sized ZrO 2 particles, located at the KNN grain junctions hinder the matrix grain growth. Additionally, the enrichment of the boundary regions of the matrix grains with Zr relative to the grain interiors, confirmed by TEM/EDXS analysis, is also a probable reason for the decreased mobility of the grain boundaries. The dielectric permittivity and losses, measured at 10kHZ, and piezo d 33 constant of KNN-ZrO 2 are 905, 0.04 and 100pC/N, respectively.