Derivation of modified Reynolds equation is obtained for the hydromagnetic squeeze films with lubricant additives on the basis of hydromagnetic flow model and Stokes Microcontinuum fluid model. An example of porous rough rectangular plates is used to guide the Stochastic modified Reynolds equation with lubricant additives and MHD effects. The equations are solved analytically using the stochastic method developed by Christensen. It is found that, there exists a critical value of the aspect ratio above which the roughness effects are more pronounced due to size effect of the lubricant additives in the presence of transverse magnetic field. Further, this critical value is dependent on the microstructure size of the additives and magnetic parameter. The coarser the microstructure, higher is the critical value of the aspect ratio in the presence of magnetic field. It is found that the squeeze film characteristics are more pronounced for rough porous rectangular plates with increasing values of magnetic parameter.