The development of information technology has led to the formation of the digital society, in which political, economic, social and other important for society processes are carried out. At the same time, the development of information technology has caused a number of ethical problems and conflicts associated with creation, dissemination and receipt of information that claims to be reliable, but not reliable. The phenomenon of post-truth holds a special place among these ethical problems and conflicts. Firstly, because everyone can face the post-truth. Secondly, because the negative consequences of post-truth can be dangerous both for an individual and for the whole society. The article distinguishes between concepts of post-truth, post-truth politics, lies and delusions. The main characteristics of post-truth, such as the illusion of reliability, based on uncritical perception of information, and the difficulty of verifying post-truth in the conditions of information overload, are discussed in this article. Some specific factors of the post-truth formation are identified and described: 1) institutional factors, which include legal and ethical-professional regulation of activities in the digital society; 2) technological factors, by which are meant those that have become possible with the development of media technologies on the Internet. The spread of post-truth has caused information disorientation, an atmosphere of distrust, ethical and other conflicts in the digital public sphere. This complicates the reflection of social reality and public discourse, which includes, among other things, the development of joint moral guidelines and the adoption of optimal decisions on socially significant issues. Ethical problems associated with the spread of post-truth are regarded as signs of a kind of crisis in the digital public sphere.