Purpose – Underdog positioning is often used to evoke a positive attitude when interacting with consumers. However, little research has been conducted on the market competition structure and innovation contexts in which underdog positioning produces the most impact. This research aims to investigate unexplored boundary conditions of underdog positioning and addresses two issues: market structures (oligopoly vs monopolistic competition) and perceived firm innovativeness (PFI). Design/methodology – Two one-way ANOVA designs (market structures: monopolistic competitions vs. oligopoly; perceived frim innovativeness: strong vs. weak) were randomly assigned to 297 graduate and undergraduate students (52 % female) majoring in business. Study 1 examined the effect of underdog positioning on consumer attitudes in the different market structures. Study 2 investigated the relationship between underdog effect and consumer attitudes through viewing conditions that varied in PFI. Findings – Drawing on the results of the study, the authors conclude that underdog positioning is effective to generate more positive consumer attitudes when employed in the market structure of monopolistic competition rather than oligopoly. Moreover, both underdog and top dog positioning are likely to generate more positive consumer attitudes when accompanied with strong PFI than weak PFI. Originality/value –This is the first study to distinguish between monopolistic competition and oligopoly market structures with underdog positioning as well as to demonstrate a positive effect of PFI, regardless of the type of brand narratives.