Thermal analysis, heating test on gram scale and simulation of exothermic behavior based on kinetic analysis has been conducted in order to evaluate thermal hazards of self-polymerization of MDI. The exothermic reactions of MDI are expected to be the polymerization which forms carbodiimide and carbon dioxide, dimerization and trimerization. When MDI is kept in adiabatic condition during 1 week (10080 hours), the simulated result shows runaway reaction can occur in the case that initial temperature was more than $130^{circ}C$. The relationship between the initial temperature (T, $^{circ}C$) and TMR is given in a following equation. TMR=$4.493{ imes}10^{-7}$ exp ($9.532{ imes}10^3$/(T+273.15)) We propose that the relationship gives important criteria of handling temperature of MDl to prevent a runaway reaction.