Using Mason’s derivation of the three‐phonon loss mechanism, the values of the coefficients of phonon viscosity (shear) &eegr; and drag coefficientsBhave been calculated for yttrium iron garnet (YIG). Further, the compressional viscosity (&khgr;) has also been calculated from the Akhieser loss phenomenon. On comparing the two viscosities (both &eegr; and &khgr;), it was found that the shear viscosity plays the prominent role in producing the damping of dislocations in YIG.