The main motivation behind the airline market deregulation in Turkey in 1983 and 2003 is to enlarge the airline market by increasing the competition. The deregulation in 1983 did not produce a significant and constructive result in the domestic routes. On the other hand the domestic market have been significantly grown due to deregulation in 2003. However it is worth investigating whether the market has grown due to the fact that new city pair markets have become part of the domestic routes or that there have been an increase in competition in previously served city pair markets. Increasing market concentration, which means that a small number of companies conduct economic activity in any market, affects competition negatively. Therefore, there is an inverse correlation between competition and market concentration which means that economic resources and activities are controlled by a few companies. High concentrated markets indicate monopoly and duopoly markets. In this study, the degree of concentration in the domestic city pair markets was measured and the situation of the increase of competition which is the main aim of the liberalization of the market entry was revealed. In this study, domestic airlines’ origin-destination passenger numbers were analyzed. The market shares of airlines for each city pair have been determined on the said numbers and based on the years 2012 and 2014 concentration values for the total 1447 city pairs have been calculated. N concentration ratio, the Herfindahl-Hirschmann Index and the Entropy Index were used to measure the market concentration rate. As a result, it has been understood that a large part of the city pair markets is monopoly, a significant part is the duopoly and very few city pair markets show oligopoly and near oligopoly characteristics. When the city pairs markets are evaluated on the number of origin destination passengers, it is concluded that the market concentration rate is high enough to affect the competition negatively.