Owing to its convenience and easy accessibility, social media is increasingly popular among healthcare professionals and has become a useful tool in the healthcare industry. Doctors' social media use patterns and online professionalism have been thoroughly studied. Various unprofessional behaviors such as excessive self-disclosure, violations of patient privacy and improper social media posts, were observed. However, studies exploring nurses' social media use and online professionalism are lacking.The objective of this study was to understand the social media use and online professionalism of Chinese registered nurses.A cross-sectional survey was adopted.Eight nursing conferences and one continuing-education program that took place in Sichuan, China.Convenience sampling was applied to select nurses who had obtained their Chinese nursing certificates, who were aged 18 years and above, and who worked in clinical settings. The final sample consisted of 658 registered nurses.Data were collected through the on-site distribution of an anonymous researcher-designed questionnaire. The questionnaire consisted of 41 items that focused on demographic and professional information, social media use and online professionalism. Medians, averages and percentages were used to describe the social media use patterns and online professionalism of Chinese registered nurses.All participants in this study were social media users and 84.5% of them believed that social media had positively influenced their clinical practice. WeChat was the most frequently used form of social media, which was used among 93.5% of the subjects. Common reasons for social media use included receiving messages from work, networking, receiving news and relaxing. Approximately 56% of the participants spent one to three hours on social media daily. Most of the participants had reposted medical knowledge on social media and had subscribed to at least one medical social media account. Additionally, 67.2% of the sample disclosed that they "often" communicate work-related information with colleagues via social media. Roughly 50% of the sample insisted that their facilities had social media guidelines. Registered nurses' professionalism was also assessed. Around half of the participants had received "friend request" from patients, while 63.5% of the sample acknowledged that there were no patients on their most frequently used social media platforms. About 7.6% of the respondents had "sometimes" posted identifiable patient information, which was much lower than the reported 32.5% rate of witnessing colleagues' disclosure of identifiable patient information. Fully 50.3% of the participants indicated that they had witnessed improper posts by colleagues.