A portable monitor for ambulatory healthcare using an i-mode cellular phone is proposed. This monitor consists of tiny unit and a cellular phone with Java platform. The unit includes a common module and a functional module. The common module provides a shared interface (analog to digital conversion, signal processing and data communication protocol conversion and etc.) for diversity of the biosignals. The functional module is replaceable and applicable to various pick-up sensors for different vital signs. An i-mode digital cellular phone with Java supported Internet browser is connected to the common module via the PDC connector. When a client signs in the i-mode server first time using his/her cellular phone, i appll (Java program for an i-mode cellular phone) will be automatically downloaded into the phone and initiated. The common module identifies which kind of signal is incoming from the functional module and then launch the corresponding software package to detect the signal. If any abnormality in the vital sign is recognized, data will be sent to specific server via an i-mode cellular phone. An interactive communication link is then setup between a doctor and a client through the wireless network.