Although friction stir welding (FSW) has widely been applied to aluminum alloys in several industries over the past three decades, it is not yet used in industry for joining of steels. The aim of this study is to characterize the microstructures and mechanical properties of FSWed dissimilar low carbon steels joint. The results indicated that the weld region is comprised of complex microstructures such as Widmanstatten ferrite, ferrite with or without carbide aggregates and grain boundary ferrite. The maximum hardness in the stir zone reached up to about 347 HV due to the solid state transformations and grain refinement. The welded plates displayed an ultimate tensile strength of about 389 MPa, which lies between the ultimate tensile strength of St37 and St52 steels, 373 and 526 MPa, respectively. Moreover, the yield strength of the dissimilar joint was found to be about 272 MPa, which is also between those of the base plates joined.