Objective:To investigate the small and dense low density lipoprotein cholesterol (sdLDL-C) level, ratios of sdLDL-C/low density lipoprotein cholesterol (LDL-C), sdLDL-C/high density lipoprotein cholesterol (HDL-C) and sdLDL-C/apolipoprotein B (apoB), and their correlation with lipid components in healthy adults.Methods:A total of 1 151 healthy adults, who underwent physical examination in Beijing Anzhen Hospital Affiliated to Capital Medical University from September to December 2020 (557 men and 594 women), were included in this study. They were divided into five age groups: 18-29 years old ( n=247), 30-44 years old ( n=269), 45-59 years old ( n=225), 60-74 years old ( n=207) and 75-90 years old ( n=203) according to the age classification standard of the United Nations World Health Organization in 2018. The levels of total cholesterol (TC), triglyceride (TG), HDL-C, LDL-C, sdLDL-C, apoA1 and apoB were measured, and the distribution of sdLDL-C, sdLDL-C/LDL-C, sdLDL-C/HDL-C and sdLDL-C/apoB in different sex and age groups were analyzed. Pearson/Spearman correlation was used to analyze the correlation between the above four indexes and other blood lipid components. Results:SdLDL-C, sdLDL-C/LDL-C, sdLDL-C/HDL-C and sdLDL-C/apoB were higher in male group ([0.56±0.23] mmol/L, 0.24±0.07, 0.49±0.22, 0.27±0.07) than those in female group ([0.48±0.18] mmol/L, 0.20±0.06, 0.36±0.17, 0.23±0.07) (all P<0.01). SdLDL-C, sdLDL-C/LDL-C, sdLDL-C/HDL-C and sdLDL-C/apoB were different among different age groups of male and female participants (all P<0.001). SdLDL-C level was significantly higher in males than in females among 18-29 years old group, 30-44 years old group, 45-59 years old group (all P<0.05). SdLDL-C, sdLDL-C/LDL-C, sdLDL-C/HDL-C and sdLDL-C/apoB were higher in males of 18-29 years old group, 30-44 years old group, 45-59 years old group and 60-74 years old group than in females of corresponding age groups (all P<0.05). The level of sdLDL-C of all participants was positively correlated with TC, TG, LDL-C, apoB, non-HDL-C and remnant cholesterol ( r＝0.50, 0.45, 0.67, 0.68, 0.61, 0.11, all P<0.01), and negatively correlated with HDL-C and apoA1 ( r＝-0.17 and -0.10, P<0.01). Conclusions:The levels of sdLDL-C, sdLDL-C/LDL-C, sdLDL-C/HDL-C and sdLDL-C/apoB in healthy adults are different in healthy adults of different ages and sex. There is a high correlation between sdLDL-C and apoB.