In this paper, the variation of unloaded Quality factor QU of a substrate integrated waveguide (SIW) resonator with the substrate parameters is presented. It is observed that the QU strongly depends on substrate thickness, dielectric constant and loss tangent values. QU of a SIW resonator is also compared with that of a conventional rectangular air filled waveguide resonator and also that of a microstrip resonator. The graphical results shown in this paper can be used as a guideline to choose a proper wave guiding structure or an appropriate substrate for SIW application especially where insertion loss is an important issue. © 2013 IEEE.