The paper investigates the relationship between entrepreneurial orientation and sustainable firm performance with the mediating role of innovation output in family and non-family businesses in the post-transition economy. In order to analyze these relationships, quantitative research on a sample of 322 Polish organizations was conducted. The research results show a few differences between family and non-family businesses concerning the influence of entrepreneurial orientation on innovativeness and sustainable organizational performance. Moreover, the study reveals the critical role of the proactiveness dimension in shaping long-term firm performance.