Aim: The aim of the present study was to assess the correlation of CA 15-3 level with Clinico Pathological parameters and molecular subtypes of breast cancer. Methods: This study was a prospective study conducted in the Department of Pathology, Government Medical College Patiala, Punjab and included 75 cases, with the approval of the Institutional Ethics Committee. Results: In the present study, patients were divided into 7 groups according to age. The highest no of cases were recorded in the 51-60 age group i.e. 5th and 6th decade (33.3%). The mean age was 50.36 ± 12.04 years. The range of age was 25 - 80 years of age. In present study value of CA 15.3 above 30 IU/L was taken as significant, it was observed that out of 75 cases, number of cases with positive CA 15.3 value are 34 (45.3%). In the present study, out of total 75 cases studied, maximum cases were noted of subtype IDC NOS i.e. 70 (93.3%) followed by Lobular (5.3%) and Medullary (1.3%) carcinoma of breast. In the present study maximum number of cases were noted in T2 stage (2-5 cm) i.e. 47 (62.7%) followed by T1 (21.3%) and T3 (11%) and minimum cases were noted in T4 stage i.e. 1 (1.3%). Out of 75 cases, maximum cases were noted in N0 stage i.e. 56 (74.6%) followed by 8 cases each of N1 and N2 (21.3%) and minimum cases were noted in N3 stage i.e. 3 (4%). Out of 75 cases, 2 cases of distant metastasis were noted. Out of 75 cases, maximum no of cases observed were of Luminal A subtype i.e. 33 (44.0%) followed by Basal (24%) and HER 2 enriched (15%) subtype. A minimal no of cases were observed in Luminal B (3%) subtype. As the tumour size increased the level of CA 15.3 also increased. p value was calculated and was found to be statistically significant between tumour size and Ca 15.3 level. (p value = <0.001). As the nodal involvement increased, the level of CA 15.3 also increased. p value was found to be statistically significant between nodal status and Ca 15.3 level. (p value = <0.001). There was a positive correlation between metastasis and CA 15.3 value which was found to be statistically significant with p value of <0.001. Conclusion: The CA15-3 levels are associated with tumor burden indicators including tumor size and lymph node status and metastasis. The higher levels of CA 15–3 are more common in patients with larger tumor size, advanced axillary lymph nodal status and in metastatic breast cancer patients. No correlation was seen with histological grade. Positive correlation was seen between serum CA 15.3 levels and luminal subtype of breast cancer. luminal A was the majority in molecular subtype and showed increased CA 15.3 levels.