We performed in vitro, animal, and human studies to clarify the effect of mayonnaise on β-carotene intake and its mechanism. In an artificial gastric juice model, we examined the transfer of β-carotene from grated carrot to mayonnaise or vegetable oil. Mayonnaise was more easily dispersed in artificial gastric juice than vegetable oil. The β-carotene concentration was greater in mayonnaise than vegetable oil. In rats, the postprandial serum β-carotene concentration in the mayonnaise group (β-carotene with mayonnaise) was higher than that in the control (β-carotene only) and vegetable oil (β-carotene with vegetable oil) groups. Continuous feeding of dietary β-carotene (14 d), employing mayonnaise or egg yolk, resulted in an increased accumulation of β-carotene in the liver. In a human study, diets were provided in the form of (1) carrot as a control (CON), (2) carrot juice (JU), (3) carrot with oil (OIL) and (4) carrot with mayonnaise (MS). Following collection of fasting blood samples, nine adult males consumed one of the four diets in random order. Fasting and postprandial changes in serum β-carotene were assessed at 2, 3, 4, 6 and 8 h following ingestion of each diet. The incremental areas under the curves of serum β-carotene concentration were higher following MS than following both CON and JU. In conclusion, we suggest that mayonnaise contributes to raising the serum β-carotene concentration when consumed with carrots rich in β-carotene, and that its mechanism is related to the emulsifying property of the egg yolk contained in mayonnaise.