¹Biotechnology Institute, Ankara University, Ankara, Turkey DOI : 10.12991/mpj.2018.54 Chlorogenic acid (CGA) is a major polyphenol in primary human diet, displaying a wide range of biological activities such as anti-oxidant, anti-inflammatory and anti-cancer effects. Several studies reported the chemopreventive effects of CGA on different types of cancers including breast cancer, which is the most common cancer among women worldwide. In this comprehensive study, we determined the anti-proliferative and cytotoxic effects of pure CGA on the phenotype of various breast cancer cell lines (MCF-7, SKBR-3, MDA-MB-231, MDA-MB-468 and BT-20) with well-defined molecular classification and characteristics, in a time and dose dependent manner by using iCELLigence real-time and label-free cell analysis technology. Cells were plated on iCELLigence system-specific E-plate L8 and treated with CGA for 72 hours at concentrations ranging from 250 μM to 8 mM. Obtained data were analyzed by RTCA data analysis software 1.0 and IC50 values of 952±32.5 μM for MCF-7, 940±21.2 μM for SKBR-3, 590.5±10.6 μM for MDA-MB-231, 882.5±12.0 μM for MDA-MB-468 and 1095±121.6 μM for BT-20 cell lines were calculated at the end of 72-hour assay. Based on our findings, CGA did not have cytotoxic activity on breast cancer cell lines, and IC50 values and growth curves displayed similar anti-proliferative patterns with slight variation. Keywords : Chlorogenic acid; phenolic compound; natural extract; breast cancer; proliferation; cytotoxicity; xCELLigence; RTCA