Objective To investigate the expressions of cystathionine-β-synthase （CBS） and cystathionine-γ-lyase （CSE） and their effects on the malignant biological behaviours of breast cancer cells， and to elucidate their mechanisms. Methods The breast cancer tissue and paracancerous normal tissue from 15 cases of patients were selected， and RT-qPCR and Western blotting methods were used to detect the mRNA and protein expression levels of CBS and CSE in breast cancer tissue， paracancerous normal tissue， MCF-7 cells， and MDA-MB-231 cells. The MCF-7 cells were divided into siNC group （transfected with siNC） and siCBS group （transfected with siCBS）， and the MDA-MB-231 cells were divided into ovNC group （transfected with CSE over-expression empty plasmid） and ovCSE group （transfected with CSE over-expression plasmid）. CCK8 assay was used to detect the proliferation activities of breast cancer cells in various groups， Transwell assay was used to detect the numbers of migration and invasion cells in various groups， and Western blotting method was used to detect the protein expression levels of E-cadherin， N-cadherin and Vimentin proteins in the breast cancer cells in various groups. Results Compared with paracancerous normal tissue， the expression levels of CBS and CSE mRNA and proteins in breast cancer tissue were increased （P<0.05 or P<0.01）. Compared with MDA-MB-231 cells， the CBS mRNA expression level in the MCF-7 cells was increased （P<0.05）； compared with MCF-7 cells， the expression level of CSE protein in the MDA-MB-231 cells was decreased （P<0.05）. Compared with siNC group， the proliferation activity， the numbers of migration and invasion cells， the expression levels of N-cadherin and Vimentin proteins in the MCF-7 cells in siCBS group were significantly decreased（P<0.05）， and the expression level of E-cadherin protein was increased（P<0.05）. Compared with ovNC group， the proliferation activity， the numbers of migratoin and invasion cells， and the expression levels of N-cadherin and Vimentin proteins in the MDA-MB-231 cells in ovCSE group were increased （P<0.05）， while the expression level of E-cadherin protein was significantly decreased （P<0.05）. Conclusion The expressions of CBS and CSE are upregulated in breast cancer tissue， and high levels of CBS and CSE promote proliferation， migration， invasion and epithelial-mesenchymal transition（EMT） of breast cancer cells.