This chapter discusses the impact of mergers as reviewed from unfair business competition. Merger is a legal act carried out by a company or more to merge with another existing company and then the merged company becomes dissolved. Merger of three banks, including Mandiri Syariah bank, BRI Syariah and BNI Syariah. The total assets of the three Sharia Banks participating in the merger vary in the following order: Bank Syariah Mandiri (BSM) with total assets of 114.34 trillion is ranked 15th, Bank BNI Syariah (BNIS) with total assets of 50.79 trillion is ranked 28th, Bank BRI Syariah (BRIS) with total assets of 49.65 trillion is ranked 30th These three companies were merged into one company, namely BSI. In an effort to merge these three companies, of course, it is regulated in the law so that unfair competition does not occur in the business world. Law Number 5 Year 1999 on against monopoly which states that ‘business actors are prohibited from merging or consolidating business entities or acquiring shares of other companies that may result in monopolistic practices and or unfair business competition’. Unfair business competition can have a negative impact from the perspective of macro management effectiveness, customer takeover, unequal distribution of shares, and unilateral termination of employee employment without severance pay.