Apolipoprotein B-48 (apoB-48) is known to be the only specific marker of intestinal chylomicron particles. The amino acid sequence of apoB-48 represents 48% of the initial sequence of apoB-100. ApoB-48 is synthesized only by the intestine in humans, while apoB-100 is synthesized primarily by the liver. Therefore, apoB-48 is a most appropriate biomarker for cardiovascular and nutritional investigation of postprandial chylomicron metabolism. In this review article, we discussed the difference between the recent findings and Zilversmit's proposal of postprandial hyperlipidemia reported over 30 years ago. The characteristics and role of apoB-48 as an apolipoprotein in chylomicrons, especially as a marker of chylomicron remnant lipoproteins, are described. The need for appropriate analytical methods to measure apoB-48 is also discussed.