Nowadays, there are so many brands that keep on emerging, which makes it quite tricky for those existing ones to survive. Matahari Department Store has been known as the only leading department store in Indonesia, as well as in Medan. However, as the years go by, there are some competitors coming, Matahari is still able to keep their customers coming back. Marketing is such a vital aspect in any businesses. Marketing is very important as it usually effects the sales of the product. With the right marketing method and tools, companies and brands will be able to obtain the results they expected. Marketing consists of many types and one of the most commonly used ones is the promotion marketing method. The main purpose of this research is basically to identify the importance of promotions in Matahari Department Store and the affect that it may caused to the customer purchase decisions. The research was conducted by using interview and questionnaires methods,then analyzed with a quantitative method..The population used is 120 correspondents, which resulting the sample to be only 92.The data obtained, was put into several tests before it gets analysed. Those data are proven to be reliable, normal and valid. From the data obtained, it can be concluded that promotion strategy does effect the purchasing power in Matahari Department Store Medan Fair. Despite the influences is known to be low, it plays an important role in effecting the sales number, which is why Matahari Department Store needs to focus more in developing more promotions method in the upcoming time in order to boost more customer power of purchasing.