Fingerprints collected from the crime scene are one of the most important evidence and have a great value in determination of individuality. Fingerprints are used to identify suspects, victims or related individual and provide leads of crime scene investigation. But fingerprints collected from the crime scene and the items of evidence of crime are mostly insufficient to determine human identification, but still they are useful to offer the informations of ridge density which are used to infer the sex determination of the unknown individual. In general, females are supposed to have a higher ridge densities than males. Characteristics of thermal ridges varies in individual, but females often have finer ridge shape and narrow space between ridges than males. The present study shows the statistically significant difference between sexes in ridge density of South Korean young population with statistical analysis of total 2000 fingerprints from 200 individuals between ages of 20 and 40 (100 males and 100 females). Epidermal ridges are counted in 5㎜ × 5㎜ section of radial, ulnar, and lower areas. The differences between sexes in ridge density is analyzed by Student's t-test and likelihood ratio for suggesting relative probabilities to infer the gender of unknown source. The results can contribute to provide a clue of forensic identification with other evidences in South Korean population.