This study provides some basic information on the improvement of diabetics' self-care activities through examining the patients' knowledge on diabetes, self-care activities, and how much they feel those activities are effective and through studying the correlation among the three factors. One hundred and fifty four patients were subjected to this study, who were treated or hospitalized in a hospital in Pusan. Researches were conducted from October 21 to November 9, 2002, and information were gathered by questionnaire and direct conversation with the patients. The data was processed through SPSS WIN 10.0 program. The Date were analyzed by descriptive statistics, ANOVA, t-test, Pearson correlation coefficient and Spearman rank correlation coefficient. The results of this study was the followings; 1) The subjects' knowledge on diabetes ranged from 6 to 23 points with a mean of 17.01 points. 2) The subjects' self-care activities ranged from 21 to 103 points with a mean of 67.72 points. That of the patients with regular treatments appeared to have the highest points (3.51) and the lowest points appeared in the measurement of sugar level in blood (2.60) 3) The subjects' feelings of effectiveness ranged from 21 to 103 points with a mean of 70.01 points. Drug therapy had the highest point (3.94) and diet showed the lowest (3.37) 4) In the general characteristics of the subjects, the more education a subject had, the more knowledge on diabetes he or she appeared to have (F=3.36, p=0.012). The self-care activities were significantly high among non-alcoholic subjects (F=4.301. p=.016). The subjects' feelings of effectiveness were higher in female patients than in male patients(t=2.132 , p=.035), and those in the ages between 51 and 60 felt more effectiveness (F=4.198. p=.003). In addition, married subjects felt more effectiveness than the unmarried (t=2.856, p=0.005), and the more education a patient had. the more effectivess he or she felt (F=2.879, p=.025). 5) In the subjects' pathological characteristic, the subjects who experienced diabetes education showed more knowledge on diabetes, more self-care activity, and more effectiveness than those without the education (t=3.193, p=.002; t=2.299, p=.023; t=2.128, p=.035). 6) As the results of the analyses of correlations among knowledge on diabetes, self-care activity, and effectiveness, the more knowledge on diabetes a patient had, the more self-care activity and the more effectiveness he or she showed (p=0.283. p=0.002; p=0.182, p=0.036). Self-care activity became higher as the feeling of effectiveness appeared higher (r=.550, p=.000). Based on the results above, several suggestions were made; 1) This study was conducted in one hospital, so it is difficult to generalize the results. It is necessary to gather more information from more patients through repeated researches. 2) The study on the other factors which can affect a patient's self-care activity is required. 3) The development of a program which improves a patient's self-care activity, knowledge on diabetes. and effectiveness is needed.