<p>The visual design of socially interactive robots influences both their perceived functions and initial impressions, such as friendliness and approachability. While a preference for humanoid over non-humanoid robots is well-documented, shape symbolism—the inherent association of object shapes with meanings—offers a promising framework for robot design. We investigated how rounded and angular shapes, combined with humanoid or non-humanoid appearances, influence human observers’ perceptions of robots’ attributes, functions, and user attitudes. Using the Implicit Association Test, we examined associations between robot shapes (rounded or angular) and attributes (friendly or potent). Results demonstrated that rounded shapes were linked to friendliness, while angular shapes conveyed potency. In a subsequent explicit questionnaire, the interactions between robot shapes (rounded vs. angular) and humanoid appearances (humanoid vs. non-humanoid) were examined. We found that rounded robots were rated as more approachable and likeable than angular ones, and humanoid robots were rated higher in service-related functions and potent attributes than their non-humanoid counterparts. Notably, individuals with stronger rounded-friendly and angular-potent associations reported lower acceptance and more negative attitudes toward modern robots and technology. These findings highlight the inherent rounded-friendly associations in robot design and suggest that humanoid appearances heighten expectations for service functionality. However, to foster broader acceptance, innovative designs that challenge stereotypical shape-attribute associations may be necessary. The interplay between rounded-friendly-companion and humanoid-potent-service associations provides valuable insights that advance the development of socially interactive robots.</p>