This study aims to determine the factors that influence people's decision to become customers in Islamic banks. And the most dominant factor influencing whether the decision of the people become customers of Islamic banks independently. The object of this study is the Bank Syariah Mandiri KCP Wirobrajan, and sample in this research is the Customer at Bank Syariah Mandiri KCP Wirobrajan. With a total sample of 62 100 respondents were selected by random sampling technique (probability). For an analysis tool used is the approach Structural Equation Modeling (SEM) with the method of Partial Least Square (PLS). Based on the analysis performed, the obtained results that the service factor (t 2,113), knowledge of the customer (3,881 t), characteristics of the bank (4,050 t), the location of the bank (2,888 t). Variables bank sale does not affect the customer's decision that proved the t value of 0.767. And in this study the most dominant factor influence the decision of the people to become customers in Islamic banks are characteristic factors with coefficient that is equal to 0.331 (coefficient characteristics of the bank is higher than other variables) and the value of R Square partially the higher of the variable that is equal to 0,483 which means that the bank characteristics affect the decision of the people become customers of islamic banks amounted to 48.3%.