The thermal behaviour of binary Cu(NO3)2 . 3H2O-Cr(NO3)3 . 9H2O mixtures in molar ratios 1:2 and 1:1 has been studied in air atmosphere in the temperature range 20-900-degrees-C. Relative thermal analysis has been used to detect the range of existence of individual intermediates in the decomposed mixtures. The intermediates have been isolated by isothermal heating of mixtures at desired temperatures and identified by IR spectrometry and X-ray diffractometry and also by standard and indirect quantitative chemical analysis. On the basis of the results obtained, a probable mechanism for the overall decomposition of the mentioned nitrates mixtures in the above temperature range is discussed.