Abstract: One advantage of the hybrid particulate collector is the electrically enhanced filtration of charged particles which escape from the electrostatic precipitation zone. The effect of the enhancement is related to particle charge. The particle charge will decay during transportation. An experimental system including the charger, flow pipe and samplers was built to measure the decay process of particle charge. Silica and fly ash particles were used. Particle net charge size distribution was in-situ measured at different samplers with the electrical low-pressure impactor in the air of relative humidity of 21%-73%. Particle charge was found to decay during aerosol flow. The charge decay rate was independent of particle composition, particle size and the relative humidity of the air. Neutralization by air ions was proposed as the main mechanism to cause the loss of particle charge. A theoretical formula to predict the time-varying net charge of a particle was derived based on Coulomb’s law and ion drift- diffusion equation. The calculated results showed good agreement with the experimental results. Theoretical analysis show that particle charge decays exponentially with time, and the decay rate increases with the ion mobility and the equilibrium concentration of ions.