Purpose:This study evaluated the surface microhardness and flexural and compressive strengths of five luting cements and compared the degree of conversion of dual and autopolymerized forms of four resin-based luting cements. Materials and Methods:Four resin composite luting cements—Panavia F, Variolink 2, RelyX Unicem Applicap, and RelyX ARC—and a polycarboxylate cement (Durelon, control group) were used in three-point bending, compression, and Vickers hardness tests following water storage for 1 week. Resin composite cements were additionally investigated with both dual and autopolymerization techniques under Fourier transformed infrared spectroscopy. Differences were analyzed using one-way ANOVA. Results:The highest flexural strengths were obtained with Variolink 2 (90 MPa, SD 22), whereas the lowest were observed with Durelon (28 MPa, SD 4). RelyX Unicem showed the highest hardness values (44 HV, SD 5), whereas Variolink 2 gave the lowest (32 HV, SD 6). The highest compressive strengths were obtained with RelyX Unicem (145 MPa, SD 32), whereas the lowest were observed with Durelon (41 MPa, SD 17). For both dual and autopolymerized groups, RelyX ARC showed the highest degrees of conversion (81% and 61%, respectively) and RelyX Unicem had the lowest (56% and 26%, respectively). Conclusion:Resin composite luting cements of similar chemical characterizations differed in their physical properties, and polymerization method influenced their degree of conversion. Int J Prosthodont 2004;17:357–363.