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Prescribed fire is an important tool for rangeland management, but variations in fire temperature and intensity contribute in part to variable ecosystem responses to fire.  This study observed peak fire temperature and fire temperature duration in over 30 prescribed head fires in mesquite (Prosopis) savanna in the Southern Great Plains, USA.  Fire temperature measurements were made at 1-sec intervals using a datalogger and thermocouples placed at -1, 0, 10, 30, 100, 200 and 300 cm relative to the soil surface.  Factors compared were summer vs. winter fires and high (2,000-4,000 kg/ha) vs. low grass (1,200-2,000 kg/ha) fuel levels. Peak temperatures and longest fire temperature duration in seconds above 100, 200 and 400 °C, respectively, were greater in summer than winter fires under low fuel conditions, but there were few significant (P ? 0.05) differences between summer and winter fires in high grass fuel.  The greatest difference between summer and winter fires under low grass fuel were found with temperature duration above 400 °C. Results partially explain why prescribed summer fires are often more effective than winter fires in achieving the management goal of top-killing invasive shrub species under marginal grass fuel conditions. Comparisons of fire temperature in interspaces between trees vs. within tree canopies are also discussed.