Reproductive life-history traits of reptiles are the important areas of animal evolutionary biology, but such studies in viviparous snakes are still scarce in China. In the current study, we detected the annual variation in reproductive life-history traits in a viviparous snake, Hypsiscopus plumbea, which was widely distributed in southern China. From 2013 to 2015, we brought 117 pregnant snakes in Wenzhou to our laboratory in July each year (2013: n = 42; 2014: n = 46; 2015: n = 29), and measured the morphological traits of postpartum females and neonates after birth. We used one-way ANOVA or ANCOVA with post-hoc Tukey’s test to compare differences in life-history traits among years, and used linear regression to assess the relationship between two variables. Our results showed that females in 2013 had largest snout-vent length (Fig. 1a) and body mass (Fig. 1b) after birth. Body condition of postpartum females in 2015, which year was hot and dry (Table 1), was worse than those of other years (Fig. 1c). Both litter size and litter mass were significantly positively correlated to maternal snout-vent length (Fig. 2a, b), but no significant annual variation was found in litter size (Fig. 3a) or litter mass (Fig. 3b). The neonatal snout-vent length and body mass were not related to maternal snout-vent length. Neonates born in 2015 had largest snout-vent length (Fig. 3c) and body mass (Fig. 3d). No significant relationship was found between offspring size and litter size. In conclusion, annual variation in morphological traits of postpartum females and neonates in H. plumbea may be related to the local climate conditions, such as temperature and rainfall. Moreover, reproductive effort and offspring size in H. plumbea may have been optimized by natural selection.