In this study, it was evaluate whether there was a correlation between the serum 25 (OH) D3 level and severity of lymphedema in patients with breast cancer.The study population was categorized two groups. Inclusion criteria of the first group were diagnosis with breast cancer-related lymphedema (BCRL) in unilateral upper extremity (n: 31). Also, second group was consist of diagnosis with unilateral breast cancer without lymphedema (n: 34). The patients in the second group were accepted as control group. The patients in the second group were not described any pain, weakness or limitation of their upper extremity secondary to breast carcinoma. Age, duration of malignancy diagnosis, side and type of malignancy, serum levels of the 25 (OH)Vit D3, calcium and phosphorus, the history of chemotherapy, radiotherapy, lymph node dissection, grade of breast carcinoma were recorded for both groups. In BCRL group, it was recorded education level, dominant extremity, side of lymphedema (right/left), duration of BCRL, lymphedema stage, body mass index (BMI) (body weight [kg]/height2 [cm2]), Visual Analog Scale (VAS), the Quick Disabilities of the Arm, Shoulder, and Hand questionnaire (Q-DASH) score, the diametric and volumetric differences between affected and unaffected extremities. Firstly, the serum levels of the 25 (OH)Vit D3 were compared between two groups. After this analysis, it was evaluated the correlations between the measurements in the BCRL group.Demographic data were similar between groups (P>0.05). In statistical analysis, it was found that the serum levels of the 25 (OH)Vit D3 were similar between groups (P: 0.188).Also, 25 (OH)Vit D3 levels were not correlated with VAS, Q-DASH, BMI, the diametric and volumetric differences in BCRL group (r<0.3; P>0.05).25 (OH) D3 vitamin level seems to be not affect BCRL. In routine clinical practice, this vitamin may not important in BCRL patients.