This paper investigated the preparation of anhydrous magnesium chloride (MgCl 2 ) from bischofite (MgCl 2 ร6H 2 O) by complex thermal decomposition method. In this process, the thermal properties of complex compound MgCl 2 รC 6 H 5 NH 2 รHClร6H 2 O, an intermediate to produce anhydrous MgCl 2 , was studied using thermogravimetry-differential thermal analysis (TG-DTA) and simultaneous thermogravimetry-mass spectrometry (TG-MS). The results showed that the thermal decomposition process of the complex combination can be divided into four stages, of which the first two stages belong to the evaporation of crystal water in the complex while the last two ones attribute to the elimination of aniline hydrochloride (C 6 H 5 NH 2 รHCl) from the complex. The weight loss for each stage of thermal decomposition was in good agreement with the existing theory. The kinetic analysis of the thermal decomposition process was performed using Coats-Redfern method and Malek method. Results suggested that the first three stages submit to 2-dimentional phase boundary mechanism (model R 2 ) while the last stage rule follows 3-dimensional diffusion (D 3 ) kinetics. The apparent active energies of four stages are 127.4, 124.8, 142.3 and 329.0 kJ mol ร1 , respectively. The frequency factors are 1.28 ร 10 18 , 7.94 ร 10 15 , 5.98 ร 10 16 and 4.39 ร 10 34 s ร1 , respectively. This study provides a valuable theoretical basis for industrializing the MgCl 2 รC 6 H 5 NH 2 รHClร6H 2 O decomposition process.