Breast cancer is one of the prevalent diseases that kill millions of women worldwide. The development of resistance and side effects of chemotherapy drugs is a common obstacle in the treatment of breast cancer. Recently, the focus of drug discovery has increased toward a valuable structure known as chalcones due to their extensive bioactivity in cancer treatment. In this study, 6 chalcones and 4 fused-pyrazoline derivatives have been synthesized (1-6) using the Claisen-Schmidt condensation technique for cyclopentanone and cyclohexanone with different aromatic aldehydes at room temperature. Chalcones 2-3 and 5-6 were used in cyclo-condensation reaction with thiosemicarbazide to form new fused pyrazoline derivatives. All the synthesized chalcones and fused pyrazoline were characterized using ATR-FTIR, H-NMR and 13C-NMR (1D ). The cytotoxic activity of these new chalcone compounds was investigated against breast cancer cell lines (MCF-7) and normal breast cell lines (MCF-10A). The results showed that compounds 1 and 10 exhibited significant antiproliferative effects against MCF-7 with IC50 values of 8 µM and 8.5 µM when exposed for 48 hours compared with the reference anticancer drug, tamoxifen. Molecular docking analysis showed that compounds 1 and 10 entered the pocket of ERα and interaction with the amino acids in high affinity of binding as tamoxifen.