Ferroelectric materials with engineered thus visible-range optical band gaps are increasingly researched in recent years, triggering potentially new applications in solar cells, opto-ferroelectric devices, multifunctional sensors, and multisource energy harvesters. To date, most band gap engineered ferroelectrics have been discovered in form of ceramics fabricated via the solid-state route. Like other functional counterparts further research of these materials into nanoscale developments, e.g., nanocomposites and thin films, demands nanofabrication methods to be investigated. An emerging band gap engineered ferroelectric composition, (K,Na,Ba)(Ni,Nb)O3−δ (KNBNNO), discovered with solid-state route has allured research for novel applications as mentioned above. However, its nanofabrication via wet chemical routes has rarely been reported. In this paper, sol–gel method is used to fabricate KNBNNO nanoparticles. The developed method can successfully form the target perovskite phases, and is able to reduce the particle size from 300 to 400 nm made via the solid-state reaction to about 100 nm. In addition, the distributed particle size in the synthesized solutions averages at 4–6 nm, making the method suitable for potential thin film fabrication. Therefore, this paper offers a nanofabrication option to the emerging KNBNNO for prospective nanoscale research. [Figure not available: see fulltext.] © 2020, The Author(s).