〔Abstract〕 Objective To simulate the tumor microenvironment though the 3D microtumor model which was constructed using droplet microfluidics.To explore its feasibility as a model for in vitro breast cancer research through3D microtumour fabrication,characterisation and sensitivity testing to chemotherapeutic drugs.Methods Breast cancer cells were encapsulated with hydrogel shells in collagen-rich microencapsulated cores to obtain breast cancer microtumours in vitro;breast cancer microtumours were co-cultured with 3D microencapsulated endothelial cells by Transwell system.The structure and growth characteristics of the microtumours were directly observed by microscopy;the CCK-8 assay was used to detect the proliferation of the cells under different culture models and the drug sensitivity to doxorubicin;flow cytometry was used to compare the differences in apoptosis during the proliferation process;and the differences in the migratory and invasive abilities of the cells were assessed by scratch assay and Transwell assay;the expression of epithelial-mesenchymal transition-related proteins was detected by Western blot.Results Breast cancer cells grew well in hydrogel nucleus-shell microcapsules;cell proliferation assays showed that 3D culture and 3D co-culture cells proliferated at a significantly lower rate than 2D culture;3D culture and 3D co-culture cells had enhanced migration and invasion ability and showed higher expression of EMT-related proteins compared to 2D culture;3D culture and 3D co-culture cells were significantly less sensitive to chemotherapeutic drugs compared to 2D culture.The sensitivity of 3D and 3D co-cultured cells to chemotherapeutic drugs was significantly reduced compared to 2D culture.Conclusion 3D cultures show similar morphology and biology to in vivo tumours and are more resistant to chemotherapeutic agents.