Temperatures in a Ural Owl Strix uralensis nest box at Hashimoto (Wakayama Prefecture) were monitored by temperature data logger (thermo recorder) during the nesting season in 2007. The temperature data from 4 March to 30 April were analyzed, and the incubation period and the hatching dates of the chicks were estimated based on recorded temperature changes. After the incubation period began, the night temperatures in the nest box was always higher than that of outside. When hatching began, the temperature in the box rapidly increased, and then the maximum temperature exceeded 20°C, sometimes 30°C. It was possible to monitor the breeding stages of the Ural Owl by use of a thermo recorder.