With a focus on the evaluation of conceptual product designs presented in the form of renderings, this paper describes an eye-tracking study in which gaze metrics, design ratings, and overall rankings of designs were measured. To explore the rationales behind fixational eye movements and numeric evaluation outcomes, additional qualitative data were collected through interviews. To investigate the predictive effect of gaze behavior on perceived design quality, we examined how fixation count and total fixation time could predict ratings of five different aspects of design (i.e., degree of innovation, aesthetic quality, realization possibility, functionality, and emotional content). Results showed that as the total time fixating on a design increased, the rating of perceived functionality of this design decreased. Design expertise and visual cognitive style were considered participant variables that are likely to influence design evaluation, and were found to be non-significant. Further analysis of the evaluation outcomes showed that the strength of correlation between the five aspects of perceived design quality varied, and that different aspects seemed not to have an equal impact on the overall rankings of design, with perceived aesthetic quality and functionality being more influential. These two aspects were also most frequently mentioned in the interviews. The findings provide valuable insights into the underlying process of design evaluation. The combined use of eye-tracking, questionnaire, and interview methods enables a richer understanding of image-based design evaluation by enriching the quantitative assessment of eye movement and evaluation outcomes with qualitative data.