MMONS(3-Methyl-4-methoxy-4'-nitrostilbene) is an organic material, which has unusually large nonlinear optical coefficients. Two methods of crystal growing were tried to prepare the crystals of high optical quality. Crystal growth from methy ethyl ketone(MEK) solution by evaporation yields crystals of limited size(10×8×8㎣) and of high lattice perfection. Phase matching directions were determined and a effective nonlinear optical coefficient was meaured and compared with that of $LiNbO_3$. The procedures for determining the optimum phase matching directions were also described.