The HIV/AIDS epidemic is a major problem around the world and an increasing percentage of new HIV cases is reported to be by sexual transmission. Many studies have been carried out in the field of peer education on HIV/AIDS among young people, however, few studies focused on the long-term effect of this education. To evaluate both the short- and long-term effects of the peer education programme, we conducted a follow-up study to evaluate the related knowledge, attitudes and behaviour intention to HIV/AIDS among senior high-school students in Shanghai, China. We selected 1950 students from 10 senior high schools in Shanghai, from whom 968 students were selected at random for the intervention group and 982 students for the control group. The same questionnaires were carried out before intervention, one month and one year later in both the groups. In the intervention group, the knowledge score of reproductive health, HIV/AIDS and sexually transmitted disease rose from 21.66 to 31.72 one month later (P < 0.001). After one year it was still 30.97, and there was no significant difference between one month and one year (P > 0.05). The behaviour intention to HIV/AIDS prevention, such as condom use during sexual intercourse also changed before and after the intervention. After both the one month and one-year follow-up intervention, we found that more students declared that they would use condoms during sexual intercourse when compared with the control group (P < 0.001). No change was seen in either knowledge or behaviour intention in the control group. These results showed that peer education on HIV/AIDS prevention among high-school students is both effective in promoting knowledge and in changing behaviour intention long term.