The development of modern Serbian competition law started in 2005 with the adoption of the Competition Act laying down rules which were generally inspired by European Union law. As is usually the case in countries in transition, the 2005 Competition Act was soon replaced by a new one, adopted in 2009. The 2009 Act further harmonised substantive competition rules with those of the EU, while at the same time empowering the Competition Authority to directly impose fines for infringements of competition law. Although it is evident that the public authorities of Serbia made certain efforts to improve competition law enforcement, it still cannot be concluded that significant progress has been made. In this paper, the authors analyse specific problems which appeared throughout six years of competition law enforcement in Serbia. Some of the problems analysed are so-called built-in errors, arising as a consequence of the choices made by the legislator. Others are, however, the result of wrongful doing by the members of the Competition Authority. Taken as a whole, they represent the main reason for the poor results achieved through competition law enforcement in Serbia. The first problem analysed is that of wrong priorities: the Competition Authority has mostly concentrated on the control of concentrations of undertakings, while generally ignoring restrictions of competition through the conclusion of anti-competitive agreements or through abuse of a dominant position. The second problem emphasised by the authors is the absence of sound economic analysis in most decisions adopted by the Competition Authority. The fining policy of the Competition Authority is also analysed in in this paper. While no fines have been imposed under the 2005 Competition Act, the Competition Authority seems to be trying to ‘catch up’ by imposing fines under the 2009 Act for infringements established in proceedings brought under the 2005 Act. The authors argue that this should be seen as an illegal retroactive application of law. The fourth problem in the enforcement of competition law in Serbia arises from a de facto privileged treatment of undertakings with state-owned capital.