The basic purpose of this study is to investigate how the traits of the buyer-seller transaction-relationship relate to relationship performance, including relationship performance explicitly in the proposed model. The traits examined include relational norm, formalization, market uncertainty, and relationship investment. It is hypothesized that relational norm and formalization have positive impacts on relationships performance while market uncertainty has a minus impact. In addition, it is hypothesized that relational norm has a positive moderating impact on the effect of relationship investment--the investment and efforts for maintaining a relationship to relationship performance. A mail-survey to the manufacturers of machinery and equipment about their relationships with the parts suppliers was performed. Data provided a strong support for the hypotheses. As hypothesized, relationship performance and formalization generally had positive impacts on relationship performance and formalization generally had positive impacts on relationship performance while market uncertainty showed negative impacts. Also, there is a good evidence for the positive moderating effect of relational norm to the impact of relationship investment on relationship performance.