The thermal dissociation of 16 pyridine complexes of the general formulas, M(py)4X2 and M(py)2X2, where M is Cu, Ni, Mn, Cd, Zn, and Co and X is SCN, Cl, Br, I and ½ C2O4, was studied by thermogravimetry and differential thermal analysis. The thermal transitions involved were mainly the depyridination reaction to lower pyridine content complexes. Such reactions as tetrakis(pyridine) → bis(pyridine) → mono(pyridine) complexes were observed. The depyridination reactions for the complexes were discussed in detail.