Heat capacity and dielectric properties of RbNbWO6 were measured as a function of temperature. The heat capacity measurements revealed the presence of two discontinuous phase transitions at 356.5 and 361.6 K. The former transition was attributed to a transition from the low-temperature tetragonal ferroelectric phase to a phase of unknown symmetry, and the latter to a transition to the cubic phase. The dielectric study revealed the presence of only one and broad anomaly below 3 10 K. The real and imaginary parts of dielectric permittivity show pronounced shifts of the maxima towards higher temperature with increasing frequency. This behaviour has been attributed to a relaxation process and it seems to be not correlated with the paraelectric-ferroelectric phase transition. (C) 2003 Elsevier B.V. All rights reserved.