PT Sun Star Motor Banyumanik located in Jalan Perintis Kemerdekaan No. 16 Semarang, the company is engaged in the field of automotive and selling car brands Mitsubishi. In the sales activities of the company using the promotional activities. The purpose of this research is to know which promotional cost variables are the most dominant influence on the volume of sales at PT Sun Star Motor Banyumanik. This research uses a multiple regression analysis, test F and test t. study using four variable promotional cost each be measured with the magnitude of the costs incurred for promotional activities, which consist of the cost of advertising (X1), the cost of personal sales (X2), cost of Publicity (X3) and sales promotion Cost (X4). While sales volume is measured by the amount of sales in dollars for one year. Results of the analysis showed a promotional cost effect on sales volume, and based on the results of multiple regression obtained Y = -1.076E10 + 553.778 X1 + 278.729 X2 + 425.572 X3 + 575.765 X4 showed that the sales promotion veriable (X 4) have the most dominant and significant influence on the volume of sales of Mitsubishi Cars in PT Sun StarBanyumanik.