In order to explain the population demography of the Vesper Rat (Nyctomys sumichrasti) and with regarding to an estimate of population size and survival rates, as well as possible differences in the movements distances between males and females, we analyzed capture-recapture data of this species from a trapping effort of 455 trap-nights and a total of 157 captures of 36 individuals which were livetraped at 3 trap heights: 3-9 m above ground (low canopy), 9-15 m (medium canopy) and the highest part of the canopy, 15-21.5 m. Due to differences between age categories in sample size, the analysis of capture-recapture histories was restricted to adult individuals. The sample of 29 adult individuals included 12 females (8 singletons and 4 captured in the complete study) and 17 males (5 singletons and 12 captured in the complete study); which represents a sex-ratio of 1:1.41, which did not differ statistically from 1:1. The capture-recapture histories were analyzed using the Cormack-Jolly-Seber model, where the best model maintains the survival constant and equal between sexes, and capture probability is constant through time, but differs between sexes. The survival probability was 0.8287, while the capture probability was 0.874 for males and 0.5733 for females. Estimated population size included 19 males and 21 females. The average distance travelled by females was 34.86 m (standard deviation 5.92) with extreme values of 20.1 to 60.32, whereas for males was 35.42 m (standard deviation 18.27), with extreme values of 10.3 to 75.1 m.