The combustion phenomena of doublet impingements of nitrogen tetroxide (NTO) and monomethylhydrazine (MMH) were studied in this research. The total flow rates of the propellants were controlled at ∼8.00 g/s to simulate the operation of a 5-lbf rocket, and the ratios of the mass flow rates (O/F) of NTO and MMH were varied from 1.0 to 2.4. With a 2-axis translation module, the thermocouple array measured the 2-D temperature distributions in the hot-fire experiments at the 20mm downstream of the impinging point. The results showed that the temperature distribution was strongly affected by O/F and mixing effect. Comparing to the previous PLIF cold-flow studies in the same conditions, the results demonstrated that the cold-flow analyses could adequately predict the position and shape of the high temperature zone in hot-fire situation. In views of the combustion phenomena, an induction period (length) to reach intensive reactions always exists, and it can be correlated to the MMH droplet size distribution or the uniformity of the MMH spray. And, a maximum length of ∼80mm of the intensive reaction zone was shown for the conditions investigated. This may be caused by the diffusion-controlled combustion in the downstream reactions.