The effect of kaolin addition on the combustion characteristics of olive residue was investigated by thermogravimetric analysis (TGA) combined with Fourier-transform infrared (FTIR) spectrometer in parallel with ash characteristics were studied by X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyzer. The experiments were carried out by burning olive residue with 2%, 4% and 8% by wt. kaolin at 900 degrees C. Results indicate that the addition of kaolin led to a decrease in the rate of weight loss during char combustion and hence an increase in CO emission. This was due to a decrease in burning quality caused by the dilution effect of kaolin in the mixture. The increase in HCl(g) and SO2(g) concentrations with kaolin addition observed in FTIR results evaluated together with XRF and XRD results demonstrates the pathway of reactions for the capture of potassium by kaolin and formation of high-melting-temperature kalsilite crystals. Potassium retention in ash was found to increase up to 4% kaolin content; however, no significant improvement in potassium retention was observed with further addition of kaolin owing to the abundant amounts of Al and Si introduced via kaolin. The results show that 4% kaolin is the optimum content at which the alkali index decreases below unity, indicating reduced tendency of fouling in combustion systems.