In this paper, we described an ultra-low power, wearable ECG system capable of long term monitoring and mass storage. This system is based on micro-chip PIC18F27J13 with consideration of its high level of integration and low power consumption. The communication with the micro-SD card is achieved through SPI bus. Through the USB, it can be connected to the computer for replay and disease diagnosis. Given its low power cost, lithium cells are used to support continuous ECG acquiring and storage for up to 15 days. Meanwhile, the wearable electrodes avoid the pains and possible risks in implanting. Besides, the mini size of the system makes long wearing possible for patients and meets the needs of long-term dynamic monitoring and mass storage requirements.