Previous research has found a positive impact of inter-firm trust on business performance and many authors have postulated that transaction costs between the firms mediates such an impact. However, literature has rarely tested this mediating effect. The objective of this research is to test such an effect. In order to do this we have developed a measurement device for transaction costs, inter-firm trust and business performance. This was then validated using an exploratory factor analysis. To test the mediating effect of the transaction costs, we analysed a set of multiple regression models using data from the tourism sector in Thailand. To further develop this research, we plan to compare the perspectives of supply chain members. We also aim to use a statistical technique called Structural Equation Model to validate all hypotheses simultaneously.