The results of measurements of the thermal conductivity dependence on temperature of pure ammonia crystal obtained in the temperature range 1.3–44 K have been shown. Quantitatively, the sample displays the thermal conductivity typical for a dielectric crystal. Below 2 K a singularity of the dependence of thermal conductivity coefficient on temperature was observed. The singularity was linked to the existence of TLS in the crystal. The analysis of the temperature dependence of the phonon mean free path in the NH3 crystal was also done.