The purpose of this research is to find out the moderating role of the reliability for BPO (Business Process Outsourcing) performances in Korean companies. Therefore, this research employed five independent variables, a moderating variable, and three dependent variables. The independent variables are business understanding, cooperation, conflict, benefit and risk share, and contact flexibility. The moderating variable is the reliability between BPO user and BPO vendor. And the dependent variables are BPO performance factors as strategic benefit, economic benefit, and technological benefit. This research employed hierarchical regression to test moderating effect of the reliability for BPO performances with 173 corporate samples. The results indicate that the reliability have significant moderating effects on strategic benefit and economic benefit, respectively. However, it is not significant on technological benefit. And the research found that the important variables depend on which types of BPO performance is considered, That is, different type of variables contribute to different type of performances. These empirical evidences could be a good guideline to the direction of business performance improvement in BPO companies, It has a limitation of R-square in the suggested model, Therefore, it is necessary to consider another important factors for improving explain power.