The long term goal of this research is to improve the fire resistance of gypsum wallboard (GWB). Gypsum wallboard consists mainly of gypsum, i.e. calcium sulfate dihydrate, CaSO4•2H2O. In buildings, the chemical, mechanical and thermal properties of gypsum wallboard play an important role in delaying the spread of fire. To build a fire resistant GWB, it is very important to study the thermal, mechanical, physical and chemical properties of regular GWB and various types of fire-resistant wallboards available commercially in the market. Various fire-resistant GWBs have been compared and contrasted with reference to a standard wallboard in this study. Regardless of the type of wallboard, the main component is gypsum. The fire resistance property is mainly attributed to the absorption of energy related with the loss of hydrate water going from the dihydrate (CaSO4•2H2O) form to the hemihydrate (CaSO4•½H2O) and from the hemihydrate to the anhydrous form (CaSO4) in a second dehydration. The present paper is a comparative study of commercially available standard, fire-rated Type X and firerated Type C gypsum wallboards. Type X wallboards are typically reinforced with noncombustible fibers so as to protect the integrity of the wallboard during thermal shrinkage, while the Type C wallboards are incorporated with more glass fibers and an additive, usually a form of vermiculite. These Type C wallboards have a shrinkage adjusting element that expands when exposed to elevated temperature. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermomechanical analysis (TMA), scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) were used to characterize and compare the materials. Various properties, such as the heat flow, weight loss, dimensional changes, morphology and crystalline structures of the gypsum wallboards were studied using these techniques.