Bus dwell time, especially in developing countries like Iran, is one of the most important factors to improve the total bus travel time, because of the high usage rate of public transportation on daily travels. This study aims to investigate the factors that affect bus dwell time, in Ardabil, Iran. The investigation was conducted among 1,267 buses, at 66 bus stops, while 20 of them are located in Central Business District (CBD) and 46 in Non-CBD. The results of data analysis showed that average bus dwell time is higher in CBD compared to Non-CBD (32.3 sec and 17.2 sec, respectively) and passengers which pay their fare with cash lead to increase the bus dwell time 2.09 and 2.22 sec/pass in CBD and Non-CBD, respectively. Two different multi regression models were estimated for two districts with regard to specified variables such as the number of boarding and alighting passengers through each door, the bus floor status, the number of passengers which used cash to pay the fare, the bus congestion and the stop congestion.