The bus network design problem is an important problem in transportation planning. It is the problem of determining a network of bus lines which best achieves a predetermined objective. This may be done with or without the presence of rapid transit lines. This study is devoted to solving this problem using genetic algorithm. The fitness function is defined as the benefit to the users of the bus network less the cost of the operator of the network, which is to be maximized subject to constraints that properly distribute bus routes over the study area. Objective function calculation depends on the basic data of the city and its bus lines and does not need traffic assignment results. So, it is calculated quickly and it makes the genetic algorithm operation faster. Several good solutions were generated through a sensitivity analysis by changing the parameters of the problem affecting bus route geographical distribution. A network assignment problem was solved for each of the alternative bus networks and several measures of effectiveness were evaluated for them. A multi-objective analysis (concordance analysis) was performed based on 10 measures of effectiveness and 14 weighting systems. As a result, a bus network was proposed for the city of Mashad, Iran.