This research aims to identify the effects of perceived product value and flow experience during product design on willingness to pay (WTP) and purchase probability in online mass customization. The participants were asked to design shoes to their taste in a custom shoe website. After the design experience, the participants were asked to complete the questionnaire. The analyses suggest that flow experience has a direct effect on consumers' WTP and an indirect effect on purchase probability through the mediating role of perceived value of mass customized products. Furthermore, perceived value of a mass customized product has a significant effect on purchase probability and no effect on WTP found in the analyses.