Website usability is reported to have crucial effects on online purchases, but few theoretical models thoroughly examine these effects. In this article, music composition theory is adopted to propose a theoretical model of website usability, based on the belief that composing good music is similar to designing a usable website. Nomological networks between three constructs of music (melody, harmony, and rhythm), cognitive and affective appraisals, and online purchase intention were examined. A field study was conducted to validate the psychometric properties of measurement items and the nomological networks for the proposed model. The study results demonstrate that the proposed model successfully explains a large amount of variance of the effects of website usability on online purchases and thus can be considered as an alternative theoretical model of website usability.