This study concerns with designing bus routes network and determining bus frequencies, while the total passenger travel time, including in-vehicle travel times, waiting times, transfer times and transfer penalties, is minimized. An iterative heuristic algorithm, modified from Lee (1998), with integrated routing and frequency setting is applied in this study. To process the significant amounts of data that are involved in the procedure and to provide graphical presentation of the resulted routes, the heuristic algorithm is embedded with the Geographic Information Systems (GIS). The procedure gives a potential result that has less total travel time of the network when compared with other studies. The algorithm has been applied to the case study, one operation zone of the Bangkok Mass Transit Authority, Bangkok, Thailand. The study area consisted of 23 zones. Compared with the existing bus network, the algorithm produced less numbers of routes and buses. The resulted routes of this study satisfied all demands within the study area, while it is not the case with the existing network.