The purpose of this study was to compare older adults with DM to middle aged adults with DM in terms of their self care behaviors and factors affecting self care behaviors. 106 middle aged adults and 60 older adults with DM participated in this study. Data were collected by a self report Questionnaire. The results were as follows: 1) Mean scores for self care behaviors of older adults were 4.73(diet) and 6.39(medication) on a 7 point scale. 2) Diet self care behaviors of older adults(mean : 5.15) were significantly higher than those of middle aged adults(4.92)((t=2.03, p=0.04), but there were no significant differences in medication self care behaviors and total self care behaviors between the two groups. 3) In older adults, self efficacy ((r=0.4890, p<0.01), self regulation(r=4694, p<0.01), situational barriers (r=-0.2668, p<0.05) , family support(r=0.2855 ,p<0.05) significantly correlated with self care behavior. In middle aged adults, self efficacy(r=0.6684, p<0.01), self regulation(r=0.3642, p<0.01), situational barrier s(r=-0.1891, p<0.06) .family support (r=0.2330, p<0.01) also significantly correlated with self care behavior. 4) In older adults, 36.16 % of the variance of self care behaviors was explanied by self efficacy (23.91 %) and self regulation(12.25 %). In middle aged adults, 48.29 % of the variance of self care behaviors was explained by self efficacy(44.67 %) and self regulation(3.62 %). This study is the first study to analyze the self care behaviors and factors affecting self care behaviors of older adults with DM in Korea. These results suggest that nurses should focus the self efficacy and self regulation in developing the nursing intervention for improvement in self care behaviors of older adults and middle aged adults with DM.