Purpose: This study aimed to identify the difference of sexual knowledge, attitudes, and behavior of college students who fulfilled military service and those who did not, for providing basic data for developing nursing interventions for the college students. Methods: This study used a descriptive research design. The subjects of this study were 3,741 male college students. Data were collected through personal interviews using questionnaires from November to December 2007. The sexual knowledge, attitudes, and behavior measurement tool was used. The collected data were analyzed by descriptive statistics, t-test and chi-square test. Results: The major findings of this study were as follows: 1) There was a statistically significant difference in sexual knowledge of contraception / abortion(p = .002, t = 3.16), venereal disease(p = .006, t = .2.73), sexual attitude of sexual behavior(p = .002; t = 3.13) and sexual double think(p = .047, t = 1.98) according to military service 2) There was a statistically significant difference in sexual behavior experience frequency of 9 items(friendship with opposite sex, kiss / embracing, petting, porno magazine / porno video contact, masturbation, sexual intercourse via anus, sexual intercourse via mouth, cause pregnancy, cause abortion: p < .000, $x^2$ = 39.47; p < .000, $x^2$ = 55.88; p < .000, $x^2$ = 46.76; p = .034, $x^2$ = 6.77; p = .017, $x^2$ = 12.05; p = .003, $x^2$ = 14.24; p < .000, $x^2$ = 47.70; p < .000, $x^2$ = 23.86; p < .000, $x^2$ = 21.84) respectively according to military service. Conclusion: The results of this study indicate that sexual knowledge, attitudes and behavior differ before and after the experience of military service, so further study for detecting military sex culture character effecting difference in sex knowledge, attitudes and behavior is needed.