Objectives: Biomonitoring is used to assess human environmental exposures. Urinary biomonitoring data are typically adjusted to a constant creatinine concentration to correct for variable dilutions among spot samples. Our objective was to investigate urinary creatinine concentrations by region, gender, age and lifestyle. Methods: We studied urinary creatinine concentrations in 6,286 Koreans aged 20 years old and older who participated the fourth Korea National Health and Nutrition Survey (KNHANES IV) in 2009. Urinary creatinine concentration analysis used the Jaffe method. Results: The average urinary creatinine concentration of 6,286 Koreans was 158.99 mg/dl. The urinary creatinine concentration was significantly higher among men (184.97 mg/dl) than women (130.02 mg/dl). In both men and women, urinary creatinine concentrations were significantly different according to age group (p < 0.01). Whereas the urinary creatinine concentration of men significantly differed with smoking in adjusted comparison analysis, that of women significantly differed by education level. Ninety-two percent of urinary creatinine concentration was included within WHO guidelines effective range(30 mg/dl ${leq}$ urinary creatinine concentration ${leq}$ 300 mg/dl). In multiple regression analysis, creatinine was influenced by gender, age and body mass index (BMI). Conclusions: The urinary creatinine value obtained from representative samples of adult Koreans aged 20 year and older in KNHANES IV 2009 could be used as a reference value for other nationally studied surveys, such as abandoned metal mine surveys and surveys for industrial complexes.