Technical Abstract: A decrease in fire frequency and past grazing practices has led to dense mountain big sagebrush (Artemisia tridentata spp. vaseyana (Rydb.) Beetle) stands with reduced herbaceous understories. To reverse this trend, sagebrush reducing treatments are often applied with the goal of increase herbaceous vegetation. Mechanical mowing is a sagebrush reducing treatment that is common applied; however, information detailing vegetation responses to mowing treatments are generally lacking. Specifically, information is needed to determine whether projected increases in perennial grasses and forbs realized and how exotic annual grasses respond to mowing treatments. To answer these questions, we evaluated vegetation responses to mowing treatments in mountain big sagebrush plant communities at eight sites. Mowing was implemented in the fall of 2007 and vegetation characteristics were measured for three years post-treatment. In the first growing season post-treatment, there were few vegetation differences between the mowed treatment and untreated control (P > 0.05), other than sagebrush cover was reduced from 28% to 3% with mowing (P < 0.001). By the second growing season post-treatment, perennial grass, annual forb, and total herbaceous vegetation was generally greater in the mowed than control treatment (P < 0.05). Total herbaceous vegetation production was increased 1.7- and 1.5-fold with mowing in the second and third growing seasons, respectively (P < 0.001). However, not all plant functional groups increased with mowing. Perennial forbs and exotic annual grasses did not respond to the mowing treatment (P > 0.05). These results suggest that the abundance of sagebrush may not be the factor limiting some herbaceous plant functional groups or they are slow to respond to sagebrush removing disturbances. However, this study does suggests that mowing can be used to increase herbaceous vegetation and decrease sagebrush in some mountain big sagebrush plant communities without promoting exotic annual grass invasion.