N,N′-Bis(2-hydroxyiminoalkyl)-α,α′-dinitrones are of interest for the synthesis of 1,1′-dihydroxy-2,2′-biimidazoles. Thermal decomposition of two these dinitrones was studied in helium atmosphere. Thermal decomposition of the studied dinitrones at temperature interval 20–500 °C consists of several steps, the first step accompanying with significant exothermic effect (700–1000 J g−1). The first step has been shown to be a two-stage process, and decomposition products have been determined using chromatography–mass spectrometry. Thermogravimetric curves were used for the kinetic studies. Kinetic parameters of decomposition are estimated within the approaches of non-isothermal kinetics (“model-free” kinetics and nonlinear regression methods), with the computer program Netzsch Thermokinetics 2.