From 1996 to 2006 Iran's population structure experienced considerable changes. During the mentioned period, the share of the population under 15 decreased from 39.6% to 28%. Considering this decrease, Iran's population was quickly guided to oldness which will have irreversible social and economic repercussions on the country's future progress. The main objective of this study is to estimate the effects of the elderly on the moving stream of other pedestrians on Iran's sidewalks, which is done for the first time in Iran using the Micro-Simulation method. The Micro-Simulation model of pedestrians is a computerized simulation procedure in which the moving behaviour of each pedestrian such as speed, path, and the direction is considered separately. According to the obtained results from this study, an increase in the percentage of the elderly population can lower the sidewalk's level of service. Also, the decrease of the average motion speed and the free walking space for wider paths is not necessarily less than that of narrow paths, in a way that by increasing the width of a sidewalk, pedestrians' total average speed and the average walking space decrease up to a specific width and then start to increase. This decrease on wider sidewalks is more than that in the narrower ones.