The theoretical torsional rigidity of 2-ply multifilament yam is derived in terms of mechanical values of its constituent filaments and yarn structural parameters as follows. Theoretical analysis shows that the specific torsional rigidity of 2-ply multifilament yarn increases with the ratio, Ψ of the filament torsional rigidity to the bending rigidity at low plying helix angle, but it decreases with the ratio at high Plying helix angle. The maximum specific torsional rigidity of 2-ply multifilament yam was observed with increase of plying helix angle at the low value of 9, but the torsional rigidity of it decreases with increase of plying helix angle at the high value of Ψ.