Despite the increasing importance of startups for countries, there is incomplete understanding of successful start ups’ bahavioural model in the entrepreneurship literature. In this vein, this research aims to analyze the behavioural model of successful startups in accelerators of Tehran. This study is applied in terms of purpose, and qualitative in terms of data gathering method. Our in-depth analysis of 12 startups with template case study strategy indicates that the behavioural model of successful startups fits the customer development model. In particular, six behavioural principles entailing focusing on problem before solution, tendency for trial and error, stating with low scale, flexibility, the simultaneous development of customers and products, and reducing the costs or affordable loss are the dominant bahaviours observed in this study. This provides valuable insights for scholars and potential entrepreneurs in regard to effective behavioural actions while starting a new business.