In the North American Northern Great Plains, Kentucky bluegrass (Poa pratensis L.) and smooth bromegrass (Bromus inermis Leyss. subsp. inermis) pose a serious threat to native grassland integrity and function. This study's objectives were to 1) determine drought resistance of non-native grassland and invaded-native tallgrass prairie during 1 and 2 yr of drought and 2) determine drought resilience of nonnative grassland and invaded-native tallgrass prairie after 1 yr of drought and 1 yr of recovery with 100% of average precipitation. Three rainout shelters, 3.6 m x 4 m, were installed on non-native and invaded-native grassland in eastern South Dakota to simulate drought conditions by excluding ambient rainfall. The shelter system was constructed on a track whereby the shelter automatically moved over the experimental plots when it rained and moved away from the plots when it stopped raining. Weekly watering treatments consisted of ambient, 75%, 100%, 125%, and 250% of the 30-yr average in 2013 and 2014 (Experiment I). Also, in 2014 a second set of the 75%, 100%, and 125% watering treatments were watered to 100% of the 30-yr average (Experiment II). Drought reduced biomass production in both non-native and invaded-native grassland sites. When plots were watered to 100% of the 30-yr average, the non-native site had similar amount of biomass compared with the drought year, but the invaded-native site had lower biomass. This response provides more evidence regarding the aggressive nature of these two introduced cool-season grasses and a mechanism to explain their continual dominance and expansion in this region.