The following complex compounds of zinc formate and urea (u), thiourea (tu) and caffeine (caf) have been prepared : Zn(HCOO)2.U.H2O, Zn(HCOO)2.2u.0.5H2O, Zn(HCOO)2.tu, Zn(HCOO)2.caf.0.5H2O and characterized by means of IR spectroscopy, chemical analysis and X-ray patterns. By means of thermal analysis the temperature intervals of the stability of the prepared compounds as well as the mechanisms of their thermal decomposition have been determined. Mass spectrometry has been used to determine the volatiles released during thermal decomposition.