Breast cancer is the most common cancer in women. Cardiovascular diseases are common complications after chemotherapy due to the effect of the drug on lipid levels. This study aimed to explore the changes in lipid profiles in patients with breast cancer under chemotherapy. Methods: In this prospective study, 50 patients with breast cancer participated. Three biochemical-lipid hematological tests were performed: total cholesterol (TC), triglycerides (TG), High-Density Lipoprotein (HDL-C), and Low-Density Lipoprotein (LDL-C) before initiation (pre-chemotherapy), at the start (1st follow-up), and at the completion (2nd follow-up) of the first cycle of chemotherapy. Statistical significance was set at p<0.05. Analyses were conducted using SPSS Statistical Software (version 22.0). Results: Mean TC values increased significantly at 2nd follow-up. TG values decreased significantly from 1st to 2nd follow-up. HDL-C was significantly lower at 1st follow-up compared to pre-chemotherapy and 2nd follow-up reaching similar to the initial levels. LDL-C values were significantly higher at 2nd follow-up compared to pre-chemotherapy measurement. Significantly positive correlations of BMI with pre-chemotherapy LDL-C, 1st follow-up TC, 1st follow-up LDL-C, 2nd follow-up TC, and 2nd follow-up LDL-C were found. Conclusions: There is a statistically significant increase in the levels of TC and LDL-C in breast cancer patients during chemotherapy. This study was not registered.