On/Off-blended learning becomes readily accessible as more on-line contents are introduced into the classroom learning. This study investigates the effects on classroom (on-class) interactions by comparing different conditions of blended learning: blended learning (on-class plus on-line with or without computer-mediated communication (CMC)) and on-class only. To do this, the study first looks into literature discussing increasing interactions: on-line contents condition, on-class grouping condition and CMC. A pre-service English education content site satisfying the conditional profile for increased interaction is provided to experimental groups of students along with CMC. The experiment was conducted in double cycles of treatment (on-class plus) and non-treatment (on-class only), and analyzed types of on-class interaction using Flanders Interaction Analysis Categories (FIAC). The findings in the comparison of blended learning (on-class plus on-line with or without CMC) and on-class only learning are: direct influence, content-related talk in particular in teacher talk is significantly reduced, initiation in students’ talk is greatly increased, and non-task-related behavior is significantly reduced.