Very little is known about the spatio-temporal ecology of the yellow mongoose Cynictis penicillata, despite this small carnivore being widely distributed in the southern African subregion. Until the present study, activity patterns and daily movement distances had only been investigated over a single season, and information on home range sizes was only available from a few populations. Here, I aimed at determining the activity patterns and the space use of yellow mongooses over the different seasons of the year in the Great Fish River Reserve (Eastern Cape, South Africa). In addition, I tested some predictions related to environmental factors (variations in photoperiod, climatic conditions and food availability over the year), as well as life cycle (reproduction) and morphological and physiological characteristics (sexual dimorphism and thermoregulatory aspects associated to the possession of an elongated body). From September 2005 to August 2011, spatio-temporal data were collected through 102 continuous tracking sessions (84 during the day and 18 during the night) of 12 adult individuals (seven males and five females) fitted with motion-sensor radio-collars. Additional data were obtained through semi-continuous tracking sessions and random locations. Yellow mongooses were essentially diurnal and crepuscular. Activity levels averaged 57 percent during the day (n = 11,807 fixes) and only 11 percent at night (n = 3,623 fixes). Yellow mongooses emerged from their burrows on average (± SD) 85 ± 62 min after sunrise (range: –11 to +369 min) and returned 21 ± 84 min before sunset (range: –518 to +225 min). The duration of the daily activity period varied between 12 min and 15 h 36 min, with a mean of 9 h 28 min. Both sexes exhibited some overground activity after sunset, but this was most pronounced in males than in females. Nocturnal activity outside the activity period was generally restricted to short underground bouts of activity occurring at anytime of the night. Diurnal resting, with up to 11 bouts per activity period, occurred in 98.8 percent of activity periods. Overall, yellow mongooses were active during 68 ± 17 percent of the time spent outside the burrow. Photoperiod acted as a zeitgeber and activity was negatively affected by adverse climatic conditions (very hot or conversely low temperatures, rain, wet soil) and probably low terrestrial arthropod activity/availability. No intersexual difference in activity levels was found, although the higher body mass of males (on average 16 oercent) implies higher metabolic demands. The total home range size (MCP 100 percent ) averaged 0.55 ± 0.65 km2 (range: 0.10–2.36 km2) and the related total perimeter measured on average 2.80 ± 1.71 km (range: 1.17–7.36 km). Male home ranges were on average more than twice large than those of females, but this difference did not reach statistical significance. However, males had larger daily home ranges (0.13 ± 0.15 km2) than females (0.05 ± 0.05 km2). In addition, daily movement distances of males were longer (1.99 ± 1.07 km) than those of females (1.29 ± 0.66 km). Males also travelled at a faster speed (0.29 ± 0.13 km/h) than females (0.18 ± 0.07 km/h). Overall, sex clearly appeared to play a role in the spatial ecology of yellow mongooses, but the underlying explanation does not seem to be linked to sexual dimorphism (body mass) or reproductive activity. Whilst the role of food availability on the space use of yellow mongooses is unclear, it is likely that low temperatures negatively affect yellow mongoose movements, as they do for their activity levels.