Although reduction of car use with the help of public transportation systems is desired, frequently stopping of minibuses and buses to board and alight passengers, affects negatively traffic flow especially when a lane is not assigned only for public transportation. The lost time, which is named as dwell time in the literature, caused by passenger boarding and alighting consists of three durations. First duration is required to stop the vehicle, second duration, defined as stop delay, is required for passenger boarding and alighting as well as doors' opening, third duration is required for the acceleration of the vehicle. Stop delays of minibuses are examined within this study. The amount of minibus stopping for passenger boarding and alighting, durations of each of these stopping and the number of boarding and alighting passengers were observed on two selected minibus routes in Istanbul. It is found that stop delay changes at peak hours and with the presence of stairs at the entrance of minibus. Additionally, it is determined that stop delay is not constant for analyzed routes. Three mathematical models are formed for minibus stop delay where the number of boarding and alighting passengers is used as independent variable. The dead time is calculated as 1.69 sec and stop delay changes 2.13 sec per passenger.