The linear viscoelastic properties of three polysilazanes with different reactive functional groups, such as Si-H, N-H and Si-vinyl groups, were investigated. The evolution of the moduli as a function of temperature was compared to data from thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Special emphasis was given to their thermal stability. The investigated polysilazanes are amorphous polymers with low molecular weight. The storage and loss modulus were measured from 75 to 150 A degrees C (dependent on the particular material), and the time-temperature superposition, following the Williams-Landel-Ferry (WLF) equation, was successfully applied. One cross-linked oligosilazane, ML33S, and the solid polysilazane called ABSE, gave typical results for amorphous low molecular weight polymers. The more reactive cross-linked oligosilazane, HTTS, showed deviating behaviour.