Variations of surface residual stresses as a function of weld runs in API 5L X70 steel plates were non-destructively monitored by Magnetic Barkhausen Noise (MBN) method. After each weld run, MBN signal and hardness distributions were recorded. MBN signals were converted into stress values by using a specific calibration procedure. The results were analyzed by considering microstructure investigations and hardness measurements, and then, they were compared with the results of X-ray diffraction measurements. MBN method seems to be a good candidate for monitoring the variation of surface residual stresses. It may also provide critical data for computer simulation and process design of welding processes.