The purpose of this study was to investigate a role of negative and positive thoughts to persuade, l b o experimental conditions (negative and positive thought conditions) were set. Immediately after the persuasion, subjects were instructed to think negatively or positively about the preceding persuasive message. In addition, a control condition was set where subjects were neither presented the persuasive message nor instructed to think. Subjects were 111 university students. 37 students were randomly assigned to each of three conditions. Experimental manipulation and measurements of dependent variables were conducted using three kinds of booklets. The result showed that negative thought instruction produced less cognitive attitude change toward the advocated position than positive thoughts instruction. It was clarified that negative thought instruction, compared to positive thought instruction, brought resistance to persuasion. The findings in this study suggested that persuasion-inhibiting effect of a forewarning may be mediated by an increase of negative thoughts and a decrease of positive thoughts.