Interactive Video Services (IVS) are a new type of media service that enables users to cast and watch videos as well as exchange messages with others. Three factors that influence IVS usage, which are technology factor, communication factor, and contents factor, were derived from the theory of interactivity. Dimensions of each factor were identified through qualitative study. We constructed a structural model of use intentions of IVS, followed by a survey conducted to statistically verify the structural model. The model reflects one of the key traits of IVS, media synchronicity, as a moderating variable. Our findings presented that each factor has a significant effect on use intentions of IVS and that the degree of effect is moderated by media synchronicity according to the differences between real-time and non-real-time IVS.