This study investigated the structural, optical and magnetic properties of BaTmxTbxFe12-2xO19(x <= 0.05) nanohexaferrites (NHFs) produced by ultrasonic assisted sol-gel combustion approach. The structure of all samples was characterized through XRD powder pattern, SEM, TEM and HR-TEM. UV-Vis diffuse reflectance studies specify that direct band gap (E-g) of pristine BaFe12O19 increases from 1.86 eV to maximum 2.55 eV due to ion substitution. The field dependent magnetization G(H) loops a 300 and 10 K were registered by applying a dc magnetic field up to +/- 10 kOe. Substitutions of Fe3+ ions by Tm3+ and Tb3+ ions affect remarkably the magnetic parameters of samples. Measured remnant magnetizations (sigma(r)) and coercivity fields (H-c) are in a range of 25.60-32.88 emu/g and 2116-4334 Oe, respectively at RT. On the other hand, estimated RT saturation magnetizations (sigma(s)) are in a range of 44.30-58.31 emu/g, and magneton numbers (n(B)) are between 8.83 and 11.72 mu(B). Magnetic parameters at 10 K have much greater magnitudes as sigma(s) = 65.11-94,12 emu/g, sigma(r) = 32.50-47.75 emu/g, n(B) = 12.96-18.91 mu(B). Coercive fields sharply decreased to a range of 720-2068 Oe at 10 K. All samples exhibit strong ferromagnetic features at both temperatures. The observed magnetic features assign that the ultrasonically produced NPs hexaferrites are suitable materials for high-density recording media and permanent magnets.