Different resistance spot welded joints of interstitial free steel have been tested by the magnetic hysteresis technique. The spot welded joints are also characterized through a peel-off test, as well as through optical and transmission electron microscopy. It is observed tlrnt the magnetic coercivity of the weld nuggets increased with increasing dislocation dmsity and precipitation. Coercivity, however, decreased with increasing nugget size and grain coarsening. The results of the study indicate that the magnetic hysteresis method could be successfully employed as a rapid and effective technique for quality testing of spot welded joints of interstitial free steels.