The Raman scattering measurement of ammonium hexachloroplumbate crystal has been presented. A second order structural phase transition from cubic (O5h) to trigonal structure (C23i) at Tc = 78 K was observed in this crystal. The Raman frequency shifts of the A1g mode of the PbCl2-6 octahedron and A1 mode of the ammoium tetrahedron have a maximum value at Tc Line splittings of the T2g mode of the PbCl2-6 octahedron, the Tzmodes of the ammonium tetrahedron and the external vibrational T2g mode have been observed below Tc, along with a soft mode corresponding to the T1g mode of the PbCl2-6 octahedron in the heigh temperature phase.