This paper presents a wearable accelerometer-based device for monitoring multiple physiological parameters of human body in sleep. Dual tri-axis accelerometers were attached on left and right chests of body for acquiring six-degree acceleration components. By using an advanced algorithm of signal processing and data fusion, the thoracic respiration, heartbeat, as well as body posture and activity were extracted simultaneously. Several experiments were conducted to validate the methodology. The developed accelerometer-based device could be applied to monitor OSA, CSA and MSA events in human sleep, and is simple, wearable, wireless, and low-cost.