Ceramic samples of the mixed system Ba2NaNb5(1-x)Ta5xO15 were investigated through dielectric measurements. Ferroelectric activity was confirmed through observation of the 50 Hz D-E hysteresis loop for samples with x greater-than-or-equal-to 0.4. As a result, the end member, barium sodium tantalate (Ba2NaTa5O15), was assigned as a new ferroelectric below the 40 K range.