Abstract: The influence of density of ZnCl₂ separation liquid, used for maceral separation, to T_max of Rock Eval pyrolysis was studied in this research. High volatile bituminous coal samples were collected from Yufeng Mine in Sanhsia, North Taiwan. The coal samples were crushed and then immersed in ZnCl₂ solution with five different density of 1.12-1.28g/cm³. Half of the immersed samples were dried after thorough water washing, another half of the immersed samples were dried without washing. All of the samples were run by Rock Eval pyrolysis afterwards. The results indicate that T_max decreases with increasing density of ZnCl₂ solution for unwashed samples. On the other hand, T_max is rather stable for wased samples. It seems ZnCl₂ solution has somekind of catalytic effect on T_max, although T_max is still the most stable parameter in pyrolysis.