Organ donation provides a life-saving opportunity for patients with organ failure. China, like most countries, is faced with organ shortages. Understanding public opinion regarding organ donation in China is critical to ensure an increased donation rate. Our study explored public concerns and attitudes toward organ donation, factors involved, and how the public pays attention to organ donation. Sixteen million users’ public information (i.e. gender, age, and geographic information) and posts from January 2017 to December 2017 were collected from Weibo, a social media platform. Of these, 1755 posts related to organ donation were included in the analysis. We categorized the posts and coded the users’ attitudes toward organ donation and the associations between the demographics. The most popular posts mentioning organ donation were “publicly expressing the willingness to donate organs.” Furthermore, 87.62% of posts exhibited a positive attitude toward organ donation, whereas only 7.44% exhibited a negative attitude. Most positive posts were “saluting the organ donors,” and most negative posts involved “fear of the family’s passive medical decision.” There was no significant gender difference in the users’ attitudes, but older people generally had a more negative attitude. Users with negative attitudes mainly distrust the medical system and are worried that the donated organs may be used in improper trading. Social media may be an important channel for promoting organ donation activities, and it is important to popularize scientific knowledge related to organ donation in order to eliminate the public’s misunderstanding of organ donation and transplantation.