Research on the board of directors tends to overlook employees and their impacts, to consider the boards as black boxes, or to highlight the outcome of the board. Although the significant institutional power of co-operative board makes decisions and organizational identities, studies on co-operative board have focused on productivity or business outcome. These have neglected how it affects the decision-making procedure of members and of how co-operative members form the identity. Thus, the purpose of this study is to illuminate the ways in which collective decision-making procedure of co-operatives is formed and implemented through ‘practice’ and ‘knowing-in-practice’. A case study was conducted using the practice theory to identify the factors that affected to build the board of directors in a worker co-operative. The research findings are two-folded. Firstly, a co-operative board is constructed by members’ practices. Secondly, constructing a co-operative board is influenced by knowing-in-practice. The implications of the study are, theoretically, it allows us to see the elements that have impacted on the composition of the board and its dynamics. Practically, we should recognize that a co-operative board is not completed instantly, but is constantly changing in the negotiation process for the organizational identity.