Reversal of the stimulus-presentation order often affects the outcome in paired stimulus comparison. Psychophysicists have found that the size and direction of the order effects depend on the compared stimuli’s magnitudes, but this magnitude dependence does not seem to have been recognized previously in cognitive research on preference judgment. The main objective of the present doctoral thesis was to investigate whether analogous valence-level dependent order effects exist for preference judgments of aesthetic preference of visual and of auditory stimuli (Study I) and of everyday objects and phenomena (e.g., Apple-Pear, Headache-Stomachache) denoted by labels and presented in a simple survey-questionnaire format (Studies II-III). An additional objective was to investigate if potential valence-level dependent order effects in Studies I-III could be accounted for using Hellström’s (1979, 2000) sensation weighting (SW) model. In Study I, there were valence-level dependent order effects favoring the second of two pleasant stimuli but the first of two unpleasant stimuli presented successively, but there were none for stimuli presented simultaneously. In Study II, there were valence-level dependent word-order effects (WOEs) favoring the left and first-read of two attractive stimuli but the right and last-read of two unattractive ones. Results were well accounted for using the SW model with a higher weight (i.e., greater impact on the comparison) for the second and the left stimulus in Studies I and II, respectively, and the valence level varying from low to high. Results of Study III indicate that the valence-level dependent WOEs in Study II were not due to the spatial positioning (left-right) of the stimuli but to the comparison being directed; the first read stimulus was compared to the second read, yielding a higher weight for the first read stimulus. The present results demonstrate robust order effects large enough to be of theoretical as well as practical relevance.