Purpose: The aim of this study was to identify factors which influence breastfeeding adaptation from among the following: parity and feeding behavior, social support, psychological, and demographic factors. Methods: The respondents were 179 breastfeeding mothers. Data were collected from June 2 to 19, 2009 at two community health centers and one pediatric outpatient department. Data were analyzed using the SPSS program and included descriptive statistics, t-test, ANOVA, correlation, and multiple regression. Results: The major findings of this study were: 1) Significant differences in the level of breastfeeding adaptation were related to number of children, current problems related to breastfeeding, and lay supporters. 2) Level of breastfeeding adaptation was significantly related to marriage satisfaction, proportion of breastfeeding, length of previous breastfeeding, planned length of breastfeeding, parenting stress, and encouragement to breastfeed given by medical personnel. 3) Regression analysis showed that parenting stress, marriage satisfaction, current problems related to breastfeeding, and proportion of breastfeeding explained 44.3% of variance for breastfeeding adaptation. Length of previous breastfeeding also explained 9.7% of breastfeeding adaptation among mothers who had breastfed an elder child. Conclusion: Mothers with lower marriage satisfaction, breastfeeding problems, and higher parenting stress require more help from their family and nurses for breastfeeding adaptation. Future research should include variables, such as mother's and baby's behavior related to breastfeeding, knowledge about breastfeeding, and attitude toward breastfeeding.