Bird-conservation organizations have long promoted the use of predator guards to increase nest success of cavity-nesting birds. Predator guards can effectively reduce nest predation, but lithium grease as a predator deterrent has never been tested. Therefore, our objective was to determine the effectiveness of lithium grease at increasing nest success. In 2017 and 2018, in Jonesboro, AR, we monitored nesting activity by Sialia sialis (Eastern Bluebird) in 148 nest boxes divided evenly among 3 treatments: baffle, grease, and no guard. Our results indicate that grease and baffles equally improved bluebird nest success by about 40%. Overall, lithium grease is a cheap and effective alternative to baffles that owners of bluebird boxes can consider using to increase bluebird nest success.