Due to rapid physical growth and psychological change, adolescence have a lot of difficulties for adjustment and mental health problem. The causes of mental diseases depend not only on individuals but also on their surrounding environment such as family, schools, economy and culture. The purpose of this study was to find out the relationship between family function and mental health of middle school students and provide basic data to develop a nursing program for prevention of mental disease and mental health promotion in adolescence. The subjects were 419 students in their first, second and third year of four middle schools located in K City. The period of data collection was from November 6th to 18th, 2000. The instruments in this study were the scale of family function and mental health. The data were analyzed by frequency, percentage, mean, standard deviation, Pearson Correlation Coefficient, t-test, ANOVA and scheffe`s test with SAS program. The results were as follows : 1. General characteristics of the subjects were examined in terms of demographic, school-related and home-related characteristics. In the demographic characteristics, the first grade was 34.4%, the second grade was 33.6%, the third grade was 32.0%, and 61.6% of the subjects had their religion. In the school-related characteristics, 52.5% answered that their school record was `average.` 76.4% of the subjects were satisfied with their school life and 92.3% kept good company. 45.3% had or have friends of the opposite sex. In home-related characteristics, 85% answered that their economic status was `average.` and 91.4% said that their parents had normal marital relationship. 84.7% of fathers and 76.9% of mothers had a minimum education of high school and 52.7% had working parents. About home atmosphere, 68.8% answered that they loved happily and 71.1% answered that they communicated well with their father and 90.5% answered that they communicated well with their mother. 2. The total score of subjects` family function ranged 4~72 points with its average of 43.5 points. Emotional function score ranged 0~36 points with its average of 21.4 points. And communication function score ranged 2~38 points with its average of 22.1 points. 3. Mental health index ranged 27~74 points with its average of 47.3 points. Self scale score ranged 6~77 points with its average of 50.2 points. Social support scale score ranged 0~36 points with its average of 20.2 points. Mental pathology scale score ranged 0~111 with its average of 43.1. 4. The correlation between subjects` family function and mental health index showed a significantly positive(r=0.478, p=.000). Emotional function showed a significantly positive correlation with the self scale (r=0.310, p=.000) and social support scale(r=0.434, p=.000); and the communication function with the self scale(r=0.326, p=.000) and social support scale(r=0.369, p=.000). Emotional function and psychopathology scale(r=-254, p=.000); and communication function and psychopathology scale(r=-0.206, p=.000) showed a significantly negative correlation. 5. There were significant differences in the state of mental health on the school year(F=6.48, P=.002), school record (F=14.94, p=.000), satisfaction with school life(F=16.35, p=.000), relationship with friends (F=13.85, p=.000); economic status(F=7.61, p=.001), home atmosphere(F=34.03, p=.000), communication with father(F=19.40, p=.000) and communication with mother(F=24.81, p=.000). The research results showed a very significant correlation between subjects` family function and mental health and it was found that school and home environment influenced on the mental health in adolescence.