We report four studies that tested the hypothesis that gratitude increases obedience. Four experimental studies (N ϭ 623) found that participants who were induced to feel gratitude obeyed to a greater extent a command to grind worms in a grinder than those feeling neutral. These novel findings demonstrate that gratitude can encourage obeying instructions to exact physical harm, violating moral principles of care. Grateful participants obeyed both benefactors and nonbenefactors. Induced happiness and admiration did not produce the same effect and we found evidence using a manipulation-of-mediator method that the need for social harmony played a mediating role. The findings suggest that gratitude can make a person more vulnerable to social influence, including obeying commands to perform an ethically questionable act.