The influence of La3+ and Nd3+ substitution for the Bi3+ cations in the low-firing Bi2Mo2O9 system is considered in regard to the sintering behavior, density, phase composition, and microwave dielectric properties. All the compositions can be sintered to high densities in temperature range of 620 degrees-680 degrees C. In (Bi(1-x)Ln(x))(2)Mo2O9 (Ln=La, Nd) ceramics, when x < 0.2 the solid solution is within a monoclinic phase (P2(1)/n) and the phase had an increase in melting temperature with the doping. In the La substitution case, the (Bi0.8La0.2)(2)Mo2O9 ceramics had the best microwave dielectric properties with a permittivity of 32.7, a Qf value (f=resonant frequency, Q=1/dielectric loss at f) of 13 490 GHz and a temperature coefficient of -4.6 ppm/degrees C. With the Nd-substituted samples, the (Bi0.9Nd0.1)(2)Mo2O9 ceramics had the best microwave dielectric properties with a permittivity of 33.9, a Qf value of 15 200 GHz and a temperature coefficient of +8.05 ppm/degrees C. The substitution of La and Nd can effectively modify the microwave dielectric properties of Bi2Mo2O9 ceramic and in particular adjust the temperature coefficient to near zero. The (Bi(1-x)Ln(x))(2)Mo2O9 (Ln=La, Nd) ceramics are very interesting new materials for an ultralow-temperature cofired ceramics technology that is compatible with Al metal electrodes.