Breast milk is the most appropriate nutrition for infants. Breast milk also benefits infants, mothers, and society, so breastfeeding is most highly regarded. However, even if breastfeeding has continuously been promoted, the rate and duration of breastfeeding has constantly declined. The objectives of the present study were to investigate duration and rate of breastfeeding in the first four months after child delivery and to determine factors related to exclusive breastfeeding during the first four months of postpartum mothers who gave birth at Maharaj Nakhon Si Thammarat Hospital. The subjects were 400 postpartum mothers who took their four-to-six-month-old infants to the ten Primary Care Units under the network of Maharaj Nakhon Si Thammarat Hospital to receive vaccination between July 1 and August 31, 2003. Data were gathered by means of interview questionnaires, focus group discussion, and observation of public health officials’ support of breastfeeding during different phases. The PRECEDE Framework was applied as the conceptual framework of the present study. Data were analyzed in terms of frequency distribution, and Chi-square test was used.