This article describes the effect of loss tangent (tanδ) values of the solvents in the stereospecific synthesis of optically active cis β-lactams under diverse microwave-induced conditions. The effects of low tanδ values of the solvents are found to be more crucial than solvents with high dipole moments and dielectric constants. Although, a significant progress of microwave-induced reactions has been registered lately, no reports have examined the tanδ values of the solvents in reactions conducted in a microwave. In this study, the synthesis of hydroxy-β-lactams under microwave irradiation with diverse solvents was considered by focusing on their tanδ values. The results indicated that for the synthesis of β-lactams solvents with low tanδ and high dipole moment and high dielectric constant are necessary. Compared to DMSO (tanδ= 0.82) and DMF (tanδ= 0.16), dichloroethane (tanδ= 0.12), dichloromethane (tanδ= 0.04) and tetrahydrofuran (tanδ= 0.04) are observed to be more effective.