This paper presents our latest results on the designs, fabrication and calibration of two micro accelerometers and a convective based gyroscope, as well as their combination to create a motion sensor for inertial navigation applications. Among the two accelerometers, the first one is a 3-DOF micro accelerometer utilizing piezoresistive effect in single crystal silicon. The sensing structure consists of four sensing-beams surrounding a seismic-mass. Therefore, the sensor is smaller than the cross-beam type accelerometer. The second accelerometer is a dual axis thermal accelerometer, working based on the thermo-resistive effect of silicon thermistors in free convective regime. Since no seismic mass is used, the shock-resistance becomes very high (up to 9.0×106g). The novel structure of the thermistors eliminated up to 93% of stress induced by temperature. The dual-axis gas gyroscope proposed here is working based on the thermo-resistive effect of light-doped silicon thermistor and the force convective heat transfer. The sensor configuration consists of a gas pump and a micro thermistor sensing element, packaged in an aluminum case with overall diameter and length of 14mm and 25mm, respectively. Unlike vibrating gyroscopes reported recently in MEMS-field, our gyroscope has "no" seismic mass; therefore it can eliminate the inherent problems such as fragility, low shock-resistance, squeezed-film air-damping, etc. Moreover, since the driving power for the moving mass is not necessary, the power consumption is also reduced. Finally, an algorithm to process the signal from a system consists of a 3-DOF accelerometer and 3-DOF gyroscope is presented. In this algorithm, quaternion based calculation was applied instead of Euler angles, therefore the problems of singularity or complicated trigonometric calculations can be avoided. The algorithm can be applied for inertial navigation systems (INS).