We present a novel design of single cell-cell interaction platform for studying tumor-stromal interaction. In cell-cell interaction assays, monitoring single cell behavior is critical to study highly heterogeneous population (e.g., cancer). For example, metastatic cancer cells are typically transported as a single circulating tumor cell; therefore, tumorigenesis should be induced from a single cell because it might be quite different from co-culturing many cells. In this work, we report a microfluidic chip that allows for isolating a pair of cells by using immiscible liquid isolation. We present the method of using a semi-permeable membrane to retain secreted proteins for interaction, while maintaining the exchange of nutrition for long-term cell-cell interaction studies. We verified proliferation enhancement of tumor cells when co-cultured with stromal cells, demonstrating the feasibility of our device as a generic platform of cell-cell interaction studies.