The controlled synthesis of non-stoichiometric perovskite type oxides is of importance for fundamental and applied studies. The present contribution focuses on how data from thermal analysis, mainly thermogravimetry and X-ray powder diffraction, can be utilized for defining optimum synthesis conditions. The perovskite oxides frequently have (or are formed from binary oxides with) high stability and low reactivity. The synthesis of a homogeneous and pure reaction product is limited by diffusion controlled mass transport, and precursor materials with mixing of cations on a microscopic level are therefore needed. The decomposition of citrate precursors, the formation and decomposition of intermediates, the control of oxygen non-stoichiometry, the decomposition of the product and reactions/phase transitions on cooling are considered. As examples, thermal analysis data are provided and discussed for major steps in the syntheses of non-stoichiometric LaMO(3) (M is V, Cr, Mn, Fe, Co or Ni).