The nanocrystalline fine powders (similar to 80 nm) of (Ba1-x La (x) )(Fe2/3W1/3)(1-x/4)O-3, (BLFW) (x = 0.0, 0.05, 0.10 and 0.15) were synthesized with a combined mechanical activation and conventional high-temperature solid-state reaction methods. Preliminary X-ray structural analysis of pellet samples (prepared from fine powders) showed formation of a single-phase tetragonal system. Detailed studies of dielectric properties (epsilon(r) and tan delta) exhibit that these parameters are strongly dependent on frequency, temperature and La composition. The La-substitution increases the dielectric constant and decreases the tan delta up to 10% substitutions of La at the Ba-site, and then reversed the variation, and hence this composition is considered as a critical composition. This observation was found valid for structure, microstructures, dielectric constant, electrical conductivity, J-E characteristics and impedance parameters also. Like in other perovskites (PZT, BZT), La substitution plays an important role in tailoring the properties of Ba(Fe2/3W1/3)O-3 ceramics.