Floating cancer cells can survive the programmed death anoikis process after detaching from the extracellular matrix for the anchorage-dependent cells. Purification of viable floating cancer cells is essential for many biomedical studies, such as drug screening and cancer model development. However, the floating cancer cells are mixed with dead cells and debris in the medium supernatant. In this paper, we developed an inertial microfluidic device with sinusoidal microchannels to continuously remove dead cells and debris from viable cells. First, we characterized the differential inertial focusing properties of polystyrene beads in the devices. Then, we investigated the effects of flow rate on inertial focusing of floating MDA-MB-231 cells. At an optimal flow condition, purification of viable cells was performed and the purity of live cells was increased significantly from 19.9% to 76.6%, with a recovery rate of 69.7%. After separation, we studied and compared the floating and adherent MDA-MB-231 cells in terms of cell proliferation, protrusive cellular structure, and the expression of cyclooxygenase (Cox-2) which is related to epithelial-mesenchymal transition (EMT) changes. Meanwhile, drug screening of both floating and adherent cancer cells was conducted using a chemotherapeutic drug, doxorubicin (Dox). The results revealed that the floating cancer cells possess 30-fold acquired chemoresistance as compared to the adherent cancer cells. Furthermore, a three-dimensional (3D) double-cellular coculture model of human mammary fibroblasts (HMF) spheroid and cancer cells using the floating liquid marble technique was developed.