In the present work, sodium titanate nanotubes doped with potassium were synthesized by the Kasuga method and tested as catalysts for biodiesel production. Potassium was added to the nanotubes in order to increase their basicity and, consequently, improve their performance in the transesterification of soybean oil with methanol. In the synthesis, the NaOH:KOH molar ratio was changed from 9:1 to 7:3 in order to increase potassium loadings in the obtained nanotubular solids. Synthesized catalysts were characterized by N2 physisorption, powder XRD, scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), FT-IR, FT-Raman and CO2 temperature-programmed desorption (CO2-TPD). Obtained results showed that sodium trititanate nanotubes containing 1.5 wt. % of potassium were obtained when 10 M alkali solution with NaOH:KOH molar ratio of 9:1 was used. In this case, the proportion of sodium and potassium in the synthesized material was similar to that used in the synthesis. An increase in the proportion of KOH to 20 and 30 molar % in the NaOH-KOH solutions used in the synthesis allowed obtaining titanate nanotubes with larger potassium loadings (3.2 and 3.3 wt. %, respectively). As it was expected, potassium addition to the sodium titanate nanotubes resulted in an increase in the amount of medium and strong basic sites. Potassium-containing nanotubes showed higher catalytic activity in the transesterification reaction than the pure sodium counterpart used as a reference. The best results were obtained with the samples containing 3.2-3.3 wt. % of potassium where a biodiesel yield of about 94-96 % was obtained at 80 °C and 1 h reaction time.