Purpose: This study aims to determine the oleic acid levels of mature breast milk (6-12 months) and to analyze the differences in oleic acid levels in mature breastfeeding mothers with chronic energy deficiency (CED) and normal nutritional status. Methods: This research was conducted in July - September 2020 in the work area of the Sudiang and Sudiang Raya puskesmas, Makassar City and the research laboratory of the State University Hospital (RSPTN) Unhas. The type of research used is analytic observation with a cross-sectional study approach. The population in the study amounted to 406 mothers. The sample in this study was breastfeeding mothers with 6-12 months of lactation. The sample size was determined by using the Dahlan formula with a total sample size of 38 participants consisting of 19 Chronic Energy Deficient breastfeeding mothers and 19   normal breastfeeding mothers. The sampling technique used was purposive sampling method. Data were analyzed using the Manwithney test. Results: The average levels of oleic acid in breastfeeding mothers with nutritional status of chronic energy deficiency were 1.00 ± 0.37 and breastfeeding mothers with normal nutritional status was 0.95 ± 0.36. The results of statistical tests found no significant differences (p> 0.05) between the oleic acid levels of breastfeeding mothers in chronic energy deficiency and normal nutritional status. Most of the found levels of oleic acid in the low category (reference 1.5) are namely 94.7% in normal nutritional status and 78.9% in nutritional status of women with chronic energy deficiency. Conclusion: The average oleic acid levels of breast milk in chronic energy deficiency and normal breastfeeding mothers were still low compared to the standard. There was no difference in oleic acid levels in breastfeeding mothers and breastfeeding mothers with normal nutritional status. A further qualitative research is needed in nursing mothers whose oleic acid levels are equal or exceed the reference.