In this work, the influence of TiO2 on the vaporization of K during combustion of straw under fixed bed condition was investigated experimentally. Controlled combustion experiments with a varied amount of TiO2 in straw pellets were performed in an 8 kW pellet burner together with sampling of particles (impactor and absolute filter), analysis of the flue gas composition (Fourier transform infrared, FTIR), and chemical analyses of the collected particles and bottom ash (inductively coupled plasma-atomic emission spectroscopy (ICP-AES), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), and X-ray diffraction (XRD)). The experimental results showed that the vaporization of K from the fuel bed was significantly reduced when TiO2 was used as an additive. The vaporization of K was reduced by ∼40−50% for an optimal amount of TiO2 additive. The optimal added TiO2 for the straw used in this work corresponds to a Ti/K (wt) ratio between ∼0.6−1.0. If more TiO2 was added to the fuel, the release of K to the gas phase was not further reduced and unreacted TiO2 was found in the bottom ash.