Magnetic tunneling junctions (MTJ) have been widely used in magnetic random access memory (MRAM) and magnetic sensors for the large magnetoresistance (TMR). [1, 2] One of the major issues for high sensitivity sensors is to obtain a low switching field (Hsw). Recently various ferromagnetic metals with low Hsw, such as NiFe [3, 4] and amorphous CoFeSiB , have been selected as the sensing layer in MTJ sensors. Moreover, CoFeSiB has a lower saturation magnetization, which is also beneficial for reducing Hsw.  With CoFeSiB as the sensing layer, the sensitivity up to 40%/Oe has been achieved in MTJ sensors.  Besides the high sensitivity, the noise level of the sensor devices in the low frequency regime is an important parameter, and nanotesla-scaled detectivity has been achieved in MTJ sensors. In this work, the low frequency noise in MTJs with CoFeB/CoFeSiB composed free layer has been studied.