Purpose: The purpose of this study was to investigate the difference in serum ferritin and leukocyte regarding overweight and obese South Korean adults. Methods: This study was conducted on 5,281 subjects older than 19, according to data from the Fifth Korea National Health and Nutrition Examination Survey (KNHANES V-3), 2015. Data were analyzed using descriptive statistics, t-test, ANOVA, Scheffe s test, Pearson’s correlation coefficient, and stepwise multiple regression analysis (SPSS 24.0). Results: First, serum ferritin and leukocyte were higher regardubg obesity, followed by being overweight and within normal weight. Second, body mass index (BMI) was positively correlated with serum ferritin and leukocyte. Third, factors affecting serum ferritin were gender, and being obese and overweight. Explanatory power of the model was 26.2%. Factors affecting leukocyte were gender, obesity, being overweight, and weight change over the past year (weight gain). Explanatory power of the model was 10.2%. Conclusion: Obesity and being overweight were factors affecting serum ferritin and leukocyte, and obesity was more affected than being overweight in Koreans older than 19. In conclusion, serum ferritin was a marker of inflammation, rather than iron status, in overweight and obese Korean adults.