Since the analysis of animal behavior is a central element of ethology and ecology, it is not surprising that a great deal of research has been conducted describing the behavior of various ungulates. Most studies were conducted during the daylight hours, thus much less is known about nocturnal behavior. Detailed analyses of nocturnal behavior have only been conducted for very prominent ungulates such as giraffes, elephants, or livestock, and the nocturnal rhythms exhibited by many ungulates remain unknown. In the present study, the nocturnal rhythms of 192 individuals of 18 ungulate species from 20 European zoos are studied with respect to the behavioral positions standing, lying - head up, and lying - head down (the typical REM sleep position). Differences between species of the orders Perissodactyla and Cetartiodactyla, as well as between individuals of different age were found. However, no differences with respect to the sex were seen. Most species showed a significant increase in the proportion of lying during the night. In addition, the time between two events of “lying down” was studied in detail. A high degree of rhythmicity with respect to this quantity was found in all species. The proportion of lying in such a period was greater in Cetartidactyla than in Perissodactyla, and greater in juveniles than in adults.