A micro inertial measurement unit (muIMU) which is based on MEMS accelerometers and gyro sensors is developed for real-time recognition of human hand motions, which when combined with appropriate filtering and transformation algorithms, becomes a digital writing system that can be used to record handwriting on any surface. The overall size of our muIMU is less than 25 mm times 70 mm times 20 mm, including the micro sensors, processor, and wireless interface components. We present our progress on using this muIMU based on Kalman filtering algorithm to filter the noise of sensors, which has allowed the system to successfully transform hand motions into recognizable and recordable English characters. Our goal is to implement this system to a digital hand-writing system that can interface with PC and mobile computing devices