Due to the extremely dangerous health effects associated with the compounds of As and Se present during coal combustion or gasification plants, the determination of sorbent materials to reduce their release into the environment becomes essential. Colourless and extremely poisonous gases (AsH3, H2Se and HSe) are the most toxic compounds that can cause serious health problems, both short- and long-term. Thermodynamic equilibrium calculations using MALT program were performed to determine sorbent materials for effective chemisorptions of arsenic and selenium in gasification system. It has been shown that Al- Mg-Be- Ca- Fe-based sorbents were effective to retain arsenic and selenium in a wide range of temperatures (500 -1700 K). However, the inclusion of chlorine and sulphur in the system tend to affect the effectiveness. The presence of chlorine in the system reduced the performance of most alkali metal and Fe- based sorbents due to formation of chlorides, while the effect is less in alkali earth metal and Al-based sorbents. Most sorbents were affected by the presence of sulphur, due to formation of sulphates, except Al-based sorbents. The retention of arsenic and selenium by Al-based sorbents is achieved in wide range of temperatures investigated, probably because of its strong binding energies in various valence forces. The analyses establish the understanding of how various parameters and conditions affect sorption process and provide an effective and economic determination of the operating ranges for optimal removal of toxic elements during coal gasification that could be expensive and dangerous in real situation.