Although there have been studies of how narrative ads affect viewers' responses more effectively compared with argumentative ads, there has been very little research done to specify kinds of message factors within narrative ads. However, it is crucial to understand what message factors enhance or inhibit narrative processing in order to produce more persuasive ad messages. In this study, the main and interaction effects on narrative processing of two message factors - plot type (product-centered vs. non-product-centered) and message sensation value (MSV; high vs. low) were investigated. The persuasion knowledge model and the limited capacity of information processing model were integrated to predict and explain effect patterns. Significant main effects were found for both message factors. In terms of plot type, a non-product-centered plot showed a significantly greater level of narrative processing than a product-centered plot which activated viewer's inference of manipulation intention. MSV also had a significant main effect; narrative ad messages with high MSV led to greater narrative processing. The analyses of interaction effects between the two factors, however, revealed a change of effect direction. When viewers watched a narrative ad with a product-centered plot, high MSV demanded additional cognitive resources from the viewers and hindered them from using their cognitive resources to activate inference of manipulation intention, leading them to evaluate high MSV ads as demanding a greater level of narrative processing compared to low MSV ads. However, in the non-product-centered plot condition, ad viewers regarded high MSV as a distraction which hampered their ability to transport themselves to a dramatized narrative world and therefore they evaluated these ads as less enjoyable. Theoretical and practical implications of the findings are discussed.