Alfamart as one of the largest modern retail companies in Indonesia which continue to grow bigger, but must always strive for profits and sales volume. One of the ways is to determine the influence of product, price, promotion and location on the buying decision. This study is conducted to determine the influence of product, price, promotion and location on buying decisions and to know the most influential variable on buying decisions in Alfamart Simongan Semarang. The data are collected through questionnaires, interviews, and observation. The source of the data from this study are primary and secondary data. This research test uses equipment with multiple linear regression, the validity test and reliability, normality test, hypotheses test, partial test (T test) and simultaneous testing (F Test). The Result from t test shows that the calculation of product = 5,518, the price = 4,564, promotional = 2,293, and location = 3,417 is greater than t table of 1,971 by using an error rate of 5%. The results of this study indicates that the product, price, promotion and location has a very significant influence on buying decision. The results of the coefficient of determination (R square) is 0.510 or 51% of buying decision is influenced by product, price, promotion, and location, while the other 49% is influenced by other variables that are not observed.