In fact the changing of consumer behavior constantly demonstrates the importance of consumer research. The dynamic nature of consumer behavior causes the product life cycle becomes shorter. Proper mapping of socio-economic class of consumer is important to enable manufacturers to provide the best products according to customer wishes. The research objective is to obtain the explanation whether there is influence of the marketing mix (product, price, place and promotion) against purchase decision of Growing Up Milks (GUM) product on three socio-economic classes (lower, middle and upper) and to discover the difference and the similarity among the class. The study was conducted in Malang by using questionnaire and data processed by using Partial Least Squares as an alternative to Structural Equation Modelling. The results shows that the product is significantly influence the purchase decision of GUM across all class. Price has a significant effect on the purchase decision only at lower and upper class. Place and promotion did not significantly influence the purchase decision of GUM across all class. Variation changes in endogenous variable (purchase decision) can be explained by the exogenous variables (marketing mix), respectively 64.8% (upper), 48.3% (middle) and 49.9% (lower). Multi Group Analysis (MGA) shown that there is no significant difference between the middle and lower classes. A significant difference between the upper and middle and between upper and lower is on product and price. Upper class inclined to purchase GUM due to the quality of the product instead of design or product packaging. Price discount and lower price are not a main consideration for upper class.