Previously reported surface transformation of ferroelectric LiH3(SeO3)2 from crystalline to amorphous state at T(a) = 80-degrees-C is studied by means of the thermal analysis (DTA, TGA) and the observation of X-ray diffraction patterns. We find an endothermic reaction (DTA) as well as a reduction of the sample weight (TGA) starts at about T(a) with increasing temperature. In accordance with this, X-ray halo intensity gradually develops above about T(a) at the expense of Bragg diffraction intensity. It is concluded that the surface transformation originates from the decomposition having a long characteristic time.