Human body is the most complex organic system in nature. To understand its integrated physiological functions, it is important to recapitulate multi-cellular interactions in tissue and map networks of dynamical organ system in vitro. An ‘Organ on a chip’ is microfluidic cell culture device that contains microenvironment of living organ, which could revolutionize drug development as alternatives to animal testing. We are developing ‘organ-on-a-chip’ using multiple cell types or organoid system to emulate human organs in different physiological states. For precision medicine, we are also creating personalized organ model using stem cell source. Through human in vivo-like organ model, we develop new approach to screen drug and targeted drug delivery, and test drug and observe reactions in real time. Finally, we aim to develop safe and efficient nanomedicines which target specific physiological microenvironment.