Involving in the increasingly fierce competition, Kompas Motor Showroom needs to expand its business. Based on the interview results, there are problems associated with the marketing mix and the indication of the fluctuations tends to decrease in sales so that companies need to develop appropriate marketing strategies. This research aims to determine the effect of marketing mix to the purchasing decision of secondhand cars in Palembang, especially in Kompas Motor Showroom. The research method secondhand is quantitative research. The population are consumers who have ever bought a secondhand car in Kompas Motor Showroom in Palembang, and the amount of sample is 105. This research use Probability Sampling with purposive sampling and data analysis techniques use simple linear regression analysis. Based on the results of descriptive analysis shows that the highest value of Marketing Mix variables is in product dimension with average percentage of 78,5% and promotion dimension having low average, that is equal to 71,3%. In the variable Purchase Decision has the highest value on the dimensions of Payment Method with percentage of 81.8%. In addition, there is a brand selection dimension that has a low percentage of 71.1%. Based on the results of this research, it can be concluded that the marketing mix at Kompas Motor Showroom in Palembang is in good category, the purchasing decision on the Kompas Motor Showroom in Palembang is in good category, and the marketing mix has a significant influence on the purchasing decision variable with the influence magnitude of 23 %.