The purpose of this study is to investigate the seven-hour sexuality education program for senior high school girl students and apply it to them to find out how this program affects their sex-related knowledge, sexual attitudes, and the self-efficacy of sexual behavior practice. The ultimate goal of this study is that high school girl students are to prevent unwanted pregnancy, STD and AIDS, after attending this sexuality education program. A non-equivalent control group pretest-post test design was used for this study. The number of experimental group consisted of 80 girl students and the control group was composed of 80 girls, too. A total of 160 freshmen from two commercial girls' high schools were selected by a convenience sampling method. This study was carried out in commercial high schools located in Daejeon, Korea from July 15th to October 31st, 2002. To discover the need for sexuality education, the researcher surveyed with a pre-designed questionnaire to 160 girls from the two different commercial high schools. The sex education curriculum was developed on the basis of the need of high school girl students for sex education survey results and literature review and a teaching-learning planning model and health belief model. The experimental group was taught the sexuality education program for seven hours from October 19th to 23rd, 2002 and each period continued for 50 minutes. The SPSS(10.0) Windows statistics software was used to analyze the data, along with frequency, percentage, $X^2$-test, t-test, and paired t-test. The instruments' internal consistencies were tested by Cronbach's alpha coefficient. The results of this study were as follows: 1. The increment of sex-related knowledge score after seven hour sexuality education was significantly higher in experimental group (t=-10.88, p=.000). 2. The increment of sex-related attitude score after seven hour sexuality education was significantly higher in experimental group (t=-2.67, p=.009). 3. The increment of the practice of self-efficacy of sexual behavior score after seven hour sexuality education was significantly higher in experimental group(t=-4.95, p=.000). In conclusion, sexuality education programs based on high girl students' educational desire, characteristics of development, a teaching learning planning model, a health belief model were effective to improve sex-related knowledge, sexual attitudes and the self-efficacy of sexual behavior practice of commercial high school girl students. This result can contribute to expand the school nurse's role in the sex education area and to develop theory-based school health nursing.