Free plant sterol-supplemented mayonnaise was examined for its capacity to lower serum cholesterol and evaluation was made of its mayonnaise. This evaluation was done via a double-blind, placebo-controlled study using forty-six normocholesterolemic and mildly hypercholesterolemic Japanese persons (total cholesterol ≥ 200 mg/dL) randomly divided into two groups. The plant sterol (PS) (+) group was given 15 g mayonnaise containing 800 mg free PS daily, while the PS (-) group did 15 g mayonnaise daily for 12 weeks. Serum total cholesterol (TC) and low-density lipoprotein (LDL)-C were reduced by 4.3% and 9.2% in the PS (+) group, on completion of the 12-week period. At that time, serum apolipoprotein (Apo) B had been reduced by 3.6% in the PS (+) group, this being significantly more compared to the PS (-) group. Serum remnant-like particle (RLP)-C and Apo E did not change significantly in either groups. Decrease in TC and LDL-C with PS (+) group was greater for the serum TC ≥ 220 mg/dL subjects compared to the TC<220 mg/dL subjects. Serum vitamin A, 25 (OH) vitamin D, and vitamin K₁ underwent no change throughout the study. Serum α-tocopherol reduction was the same in the two groups. The PS (+) group showed significant increase in serum β-sitosterol while β-sitosterol remained within normal range throughout the study period. For complete blood count (CBC) and blood biochemistry, all values were normal in the two groups. Free plant sterol-supplemented mayonnaise is thus shown a safe food for reducing serum TC and LDL-C. This mayonnaise should prove applicable for reducing serum LDL-C in mildly hypercholesterolemic persons.