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Eggshells are among the emerging hazardous waste from the food processing industry. This work sought to valorize waste guinea fowl eggshells. Guinea fowl eggshells (GFEs) were evaluated in the production of CaO for chemical and industrial application. The functionality, thermal stability, elemental composition, phase distribution and surface morphology properties of uncalcined GFEs and GFEs calcined at 700°C, 800°C, 900°C, 1000°C and 1100°C were systematically studied by FTIR, TGA, XRF, XRD and SEM-EDX respectively. The elemental analysis revealed Ca as the main element in the GFEs. The uncalcined GFEs showed intense peaks that corresponded to calcite (CaCO3) phases. These transformed into Ca(OH)2 as the temperature of calcination increased and finally to CaO in the FTIR analysis. In the XRD diffractograms, the main peaks at 2θ values were 29.466° for the uncalcined GFESs and at 37.377° for the sample treated at 1100°C. The phases were confirmed as CaO when compared with JCPDS files. Using the Scherer equation, the CaO crystallite size for the sample calcined at 1100°C was found to be 50.68 nm along the (2 0 0) orientation. All the samples showed multi-step decomposition patterns in the thermogravimetric analyses (TGA), with weight loss of up to 47% for the uncalcined GFEs sample, which was mainly due to the transformation of the calcite (CaCO3) phase to CaO by removal of bound water, organic components, and CO2. Samples calcined at 1100°C showed mainly CaO phases in XRD analyses and fairly stable with 7% loss in weight after treatment at 800°C. SEM images of samples calcined at 900°C …