Microhabitat use beneath the canopy of perennial woody plants by the heliothermic sleepy lizard (Tiliqua rugosa) was examined at a site near Mt. Mary in South Australia by testing whether the position adopted by lizards under bushes was influenced by their state of activity, time of day, or month. Thirty radio-tagged lizards were followed in 2000 during their spring period of activity (September–November). Lizard position beneath a plant canopy (one of nine sectors) and behavior were recorded for each observation (radio-tagged or random encounter). Active and inactive lizards showed nonrandom use of sectors beneath plant canopies: using mainly the center and north, northeast, and east sectors (northeast quadrant), but this changed with season. Temperature changes beneath plant canopies were measured, these resulted from diurnal and seasonal shifts in the sun's position. Temperature gradients in the north-south and east-west axes of bush canopies were shown to shift with time of day and season. Sector use by lizards reflected changing thermal conditions beneath plant canopies. When ambient conditions were cooler, lizards used the warmest northeast quadrant in the morning and the northwest quadrant in the afternoon. During hotter periods of the year lizards were found most often in plant centers. Proportion of records in the center and the southwest increased from September to November, whereas those in the north and northeast decreased over that period. Microhabitat use changed with lizard activity. Active lizards were found less often than inactive lizards in the center of bushes. Inactive lizards tended to avoid southern and western facing sectors. We suggest that, during the extended daily periods of inactivity, sleepy lizards are either selecting a position that has preferred microclimatic conditions within temperature gradients of canopies, or they may have evolved a preference for north and east facing sectors because of a consistent thermal advantage over the course of the changing daily thermal regime in a heat stressed environment.