Abstract: Abstract: The law of diminishing marginal utility is one of fundamental theorems of economics. It reveals a phenomenon that the marginal utility tends to diminish when people continually consume one same commodity. The law has been confirmed to exist in varied fields, while no previous research has investigated its existence in visual perception. In this study, we conduct a controlled experiment to investigate the existence of diminishing marginal utility in visual perception. We recruit participants to estimate the correlations of a set of scatterplots by visual perception. We record the perception bias and completion time of each trial, and then apply the cardinal utility theory to quantitatively analyze the marginal utility occurred in the experiment. The results confirm that the law of diminishing marginal utility exists in the correlation perception of scatterplots; the participants tend to underestimate scatterplot correlation; no significant difference exists between the participants majored in visualization and other professional backgrounds in terms of perception bias and completion time.