We have determined the density, dynamic viscosity, and surface tension of liquid phase Beckmann rearrangement mixtures, consisting of e-caprolactam and fuming oleum. These important properties have been measured in wide ranges of both temperature and molar ratios of acid and e-caprolactam, covering conditions that are of relevance for industrial production of e-caprolactam from cyclohexanone oxime, i.e., T = (293 to 393) K and ([H2SO4] + [SO3])/[e-caprolactam] = (1.4 to 2.6). The results were correlated as functions of temperature and composition. The density of oleum/e-caprolactam mixtures shows a linear relationship with both temperature and composition. A modification of the traditional Reynolds model proved to be the most suitable way to represent the dynamic viscosity of these Beckmann rearrangement mixtures. The reduction of the surface tension with temperature is described with a power law expression, while the decrease of the surface tension with increasing molar ratios of acid over e-caprolactam is described with a linear relationship. These results can be applied to design liquid phase Beckmann rearrangement processes on both large scale and microscale.