The mechanical properties of transformation-toughened ceramics of the composition ZrO2 + 12% CeO2 with additives of CaO, Y2O3, and Nb2O5 in an amount of 1% (molar fractions) have been studied. Doping increases the strength and cracking resistance of the material. The increase of strength is due to grain refinement in the material. According to their effect in increasing the strength (and in decreasing the average grain size), the doping elements considered can be arranged in the sequence Ca, Y, and Nb. As regards their effect in increasing the critical coefficient of stress intensityK1c (measure of cracking resistance), the doping elements can be written in the following order: Ca, Y, no additive, and Nb. The level of cracking resistance of the material correlates with the volume of the elementary cell of the tetragonal solid solution. It is shown that cracking resistance increases due to the more intensive destabilizing effect of a doping an additive on the tetragonal solid solution. The highest effect in increasing the strength (from 380 N/mm2 for a material without an additive to 680 N/mm2 for one with an additive) and the cracking resistance (from 15 to 23 N/mm3/2) is produced by CaO. Recommendations on the selection of doping elements are given.