The background of this research with the advent of globalization, which brings a modern retail to thrive and eventually become increasingly keen competition in the modern retail industry in Indonesia. The emergence of new players in this industry increasingly tightening competition. There are interesting from the consumer behavior in modern retailing, most shoppers in modern retail shops in big cities like Jakarta, Bandung and Surabaya experience impulse buying (unplanned purchasing) when shopping. This study tried to determine what factors cause consumers impulse buying. This study use 2 independent variables, that are positive emotions (X1), store atmosphere (X2) and impulse buying as the dependent variable (Y). After doing a literature review, and preparation of the hypothesis, the data were collected through a questionnaire distributed to 60 people in the Alfamart Tirto Agung Semarang, which has made a impulse buying with purposive sampling. While the analysis of the data processing is done by using SPSS 20.0. Analysis were performed with existing data using a test of validity, reliability, normality test of multiple regression analysis, hypothesis testing using the f test and t test, and koefisien determination. Based on the calculations using SPSS version 20, the results of this research showed that the regression equation Y= 17,095 + 0,144X1 + 0,425X2 + e. In addition, the F test result of 10,281 which was bigger than F table was 3,16. Similarly to the F test, the T test result was bigger than T table and had a significance less than level significance of 0,05. So, it can be consists of positive emotions (X1) and store atmosphere (X2 had a positive and significance influence to impulse buying (Y). The most influence variable is store atmosphere (X2) with the highest regression coefficient of 0,425.