Application of tailor welded blanks (TWBs) in automobile industry and aircraft manufacturing have been increased during past few years. Efficient material distribution and decreasing weight of the final part are some of the most important advantages of TWBs. Since tailor welded blanks are produced with at least two dissimilar and uniform or non-uniform thickness materials, they show different behavior than uniform materials during deep drawing process. In this research, the effect of weld line orientation on formability in deep drawing of tailor-welded blanks is examined using finite element simulation and experiments. The thinning behavior of the circular TWBs during a deep drawing in a square die is studied for different weld line orientations between two mild-steel blanks with different thicknesses. The numerical and experimental results indicate that the orientation of the weld line direction of the blank sheet has significant influence on the deformation behaviour. It is seen that thinning behavior is similar for two sections of TWB for the same weld line orientation. In addition, the most thinning occurs at 45 degree rotation of weld line, thus appropriate weld line orientation or the tailor blank sheets direction orientation can improve the formability of the tailor-welded blank in a deep-drawing of square cup.