The purpose of this study was to test and to compare, in vitro, the sealing ability of four different cavity varnishes used to minimize the marginal leakage of amalgam fillings. For this purpose, a model was developed in order to avoid quality-deteriorating effects (such as condensation forces used during placement of amalgam) and temperature changes. In this model, raw ceramic disks were used instead of dentin. The four varnishes showed significant reducing effect on the penetration of the dye (Methylene Blue) compared with the control. There was no cavity varnish with optimal sealing.