Social media has recently expanded dramatically, as more people are using different media such as blogs, Facebook and Twitter, to express their opinions. This increases the possibilities to spread information and an unclear legal regulation in this area can create adverse consequences. Freedom of expression is a constitutional right, which forms an important cornerstone of a democratic society. Public employees’ freedom of communication means that they can submit information to the media, without fear of reprisals from the authorities. The right does not mean that it frees the employees from their duties of loyalty to their employer and to follow the employer's decisions and directives. This jurisprudential thesis aims to clarify the legal guidelines for a relatively talked about problem, concerning how freedom of expression restricts the duty of loyalty in the public sector. Initially, unlawful restrictions on public employees' speech is reported to give the reader a better understanding of what is legally permissible legal action for an employee to take in these contexts. From a legal dogmatic method, the applicable law will be analyzed and provide answers to my main question: Under what conditions can public employees express themselves in social media and how does these statements relate to the employee's freedom of expression and the duty of loyalty? Public employees’ has a relatively high ceiling, in terms of what they can express themselves about in social media, which is largely due to the freedom of expression restricts the duty of loyalty in the public sector. In my judgment, stronger protection for whistleblowers in the Swedish legal system is required, since many employees are afraid of becoming victims of reprisals. Introduction of an enlarged protection of integrity, outside the scope of the YGL and TF, may also be necessary, since many social media falls outside the database rule and if violation occurs here it lapse protection. A new fundamental law on freedom of expression (NYGL) will hopefully contribute to increased understanding of the guidelines on social media usage. In the future, employers should focus on clearer policy in this area and also a clearer understanding of why freedom of speech is so valuable.