Little is known about many aspects of the ecology of the Desert Nightsnake (Hypsiglena chlorophaea). I studied the ecology of H. chlorophaea from 121 specimens collected May to October 2004 and 2005 in central Washington State. In this region, males ranged in size from 184–382 mm SVL (283.7 ± 5.8 mm, N  =  49), whereas females were 158–532 mm SVL (335.5 ± 69.4 mm, N  =  58). Body mass of males was 2.6–22.1 g (10.2 ± 5.04 mm) and females 2.3–53.9 g (15.1 ± 9.49 mm). In Washington, H. chlorophaea feeds on a wide variety of prey such as scincid and anguid lizards, thamnophiine snakes, anurans, and the eggs of other squamate reptiles. In addition, I report the first mammalian prey item taken by H. chlorophaea. The reproductive ecology differs little from other parts of the range of H. chlorophaea. Males (N  =  22) with enlarged testes were found from mid-May through late August. Females (N  =  17) with enlarged follicles and ova were found from May through June, with recent hatchlings collected during mid-August. Based upon these data, in Washington, H. chlorophaea has a more varied diet compared to southern populations but shows a similar preference for lizards. With regard to reproductive patterns, Washington populations of H. chlorophaea differ very little from other populations.