Since the Olympics, the biggest sport event takes place every four years, the performance evaluation in these four years is important for countries. The purpose of this paper is to calculate the performance and ranking of countries participating in the London 2012 Olympics using DEA(linear program). The data collection was made for the participating states, inputs included the population of the participating countries, the athletes and the results of the previous period) and outputs also included the total medal count. For each type of medal, according to the previous studies, a fair index was specified (Gold,10;Silver,2;Bronze,1).Then, performance of each country was calculated using the DEA and EMS software and countries were ranked with efficiency and inefficiency factors. Results showed that although some countries (USA, China, and Great Britain) attained high ranks in the Table Games, they had lower ranks in the Efficiency Table (sixth, seventh, eighth). Teams like Iran, Jamaica and New Zealand's gained the top rates in the performance table (1, 2, 3), yet they received 15, 17 and 18 ranking in Olympics Table. So we can say that top ranking in Olympic table may not be equal to the optimal performance of teams.
