Several aspects of natural history of Blaesodactylus ambonihazo, a gecko distributed in a dry forest of northwestern Madagascar, were investigated in the rainy and dry seasons between 2000 and 2006. There were no significant sexual size differences in snout-vent length, and no sexual dimorphism was detected either in head width or body mass. Females ceased oogenesis during the rainy season and were recrudescent at the beginning of the dry season. They probably lay eggs in the middle of the dry season. Hatchlings were observed at the beginning of the rainy season and probably reach adult size in the subsequent dry season. At night geckos perched on tree trunks and buildings and exhibited typical sit-and-wait foraging. During the day they retreated to shelters, mainly crevices between buttress roots. The gecko was thermally passive to environmental temperatures, showing a wide range of cloacal temperatures (15–30 C), but they selected relatively higher substrate temperatures at low air temperature, possibly for thermoregulation. Because multiple individuals were observed on single trees, home ranges of the gecko were presumably overlapping each other, and no obvious territorial behavior was observed. The absence of male-biased sexual dimorphism, which suggests little male-male competition for mating, also supports the absence of territoriality of B. ambonihazo. Comparison with a syntopic diurnal gecko, Phelsuma kochi, which shows ecological characters similar to B. ambonihazo but has exclusive home ranges, may clarify ecological correlates associated with temporal niche partitioning.