Proton conductivity of the natural diatomite was studied by AC complex impedance technique. At room temperature, the highest proton conductivity was found to be 4.5 10-7 S·cm-1. By hydrating the diatomite, the proton conductivity was increased by two orders of magnitude. The room temperate proton conductivity of the hydrated diatomite (5.5 10-5 S·cm-1) was comparable to other hydrated solid proton conductors. Based on these results, the natural diatomite could be used as solid proton conductor for various electrochemical applications such as fuel cells, gas sensors, humidity sensors, and pH sensors.