P2P lending is a service that lender and investors directly trade online, and have become a new investment and loan for financial consumers. This study focuses on the fact that as P2P transactions adopt the trading method of crowdfunding and reverse auction, investors’ decision-making method changes significantly. Despite the percentage of goal(transaction) information and reverse auction method the fact that investors can’t know their prices each other is a key factor causing uncertainty in P2P investment. This study derived the following investment behavior results through the analysis of the Seemingly Unrelated Regression (SUR) model with instrumental variables using data from the US P2P platform Prosper (prosper.com). First, as the percentage of goal increased, the number of investors recruited increased. Second, the higher the percentage of goal, the higher the investment interest rate offered by the investor. Contrary to the expectation that the more investors gather in the reverse auction price determination method, the lower the interest rate due to intensifying competition, it shows the opposite result. This is based on changes in the decision-making of investor groups who perceive uncertainty at different levels when investing in P2P. In other words, the group of investors recruited varies depending on percentage of goal, and the decision-making of the investment price also varies depending on the group of investors recruited. This study is the first to consider the determination of the interest rate in a P2P investment decision study, and it is significant that the consumer behavior theory was applied to investment behavior.