PT Sumber Alfaria Trijaya Tbk is one of the companies engaged in modern retail with Alfamart store as stores. Consumer Buying decision is one measure that can describe the performance of the company's existence. The purpose of this study is to investigate the Influence of Psychological Factors, Cultural and Situational to Consumer Buying Decisions in Alfamart Stores in Ngaliyan District, Semarang. To get the appropriate results, this study uses Statistical methods such as multiple linear regression method, T-test , F test and the coefficient of determination (R2). Based on the results of multiple linear regression equation Y = 1.673 + 0.227 (X1) + 0.263 (X2) + 0,305 (X3) . Based on the the analysis t value of variable psychological factors is (2.404), cultural factors is (2.901) , situational factors is (4.480) having a value greater than t table (1.660) . ANOVA calculation results are known that the calculated F value (40.980) is greater than F table (2.700). Then it can be concluded that these three variables partially and simultaneously influence purchasing decisions. And situational factors (X3) have strong dominant influence on purchasing decisions.