The spatial ecology of animals is influenced by a combination of factors. Spatial ecology parameters are commonly calculated for rattlesnakes of the genus Crotalus, but they are highly variable within and among populations and species. Rattlesnake movements can be influenced by sex, body size, season, and abiotic factors, but the relative importance of each still remains unknown. We quantified aspects of the spatial ecology of a population of Northern Pacific Rattlesnake (Crotalus oreganus oreganus) in the southern part of its range in order to determine the factors that influence its spatial ecology. We found that males had larger home range sizes than females for the entire 14-month study. However, sex differences in movements were present during the spring mating season but not the summer post-mating season, suggesting that male mate searching causes males to have larger overall home ranges than females. We also found that body size was not related to home range size, but this effect was sensitive to the inclusion of two outlier males. Our seasonal analyses revealed that outside the mating season, male body size was negatively related to mean daily movement, while female body size was positively related to mean daily movement. In the spring, larger males made their first long distance movement earlier than smaller males, suggesting that body size may influence the timing of mate searching activity. Our study shows that sex and season, which are influenced by the mating system, are important factors that determine the spatial ecology of C. o. oreganus.