Purpose: The aims of this study were to assess changes in the microhardness and surface roughness of a dual-cured composite resin cement after water storage for different periods of time. Materials and Methods: Sixty specimens were divided into four groups comprising high- and low-viscosity cement specimens stored eithe dry or in water for 1 to 60 days. Microhardness and surface roughness measurements were made after 1, 7, and 60 days of storage. Results: It was found that although interactions complicated the interpretation of the results, the water-stored samples had a significantly lower microhardness compared to the dry-stored specimens for every time interval. In addition, the high-viscosity specimens had a significantly higher microhardness compared to the low-viscosity specimens. An increased microhardness was found for all groups, except for the low-vis cosity, water-stored specimens after 60 days of water storage, which was attributed to an effect of the chemical postcuring process. Although difficult to evaluate from a clinical point of view, the laser profilometry analysis revealed that a significantly increased surface roughness was found after water storage and increased storage time that was possibly caused by a deterioration of the resin-matrix surface. Conclusion: For the permanency of the interfacial luting material, a high microhardness value seems to be important.