Is it illegal to use Twitter in Chinese mainland?

It's not illegal. According to official website, a query about Baidu's legal service, there are some legal issues that need to be observed during the use. In China, the Internet is regulated, and the use of any form of online activities needs to comply with the laws and regulations of China. Using illegal or immoral language or behavior may violate relevant laws and regulations and lead to punishment. Therefore, when using social media platforms such as Twitter, we should abide by relevant laws and regulations and social ethics, respect social interests and not engage in illegal and criminal acts.