The effect of solid particle loading on the collection efficiency of a single-stage impactor with different impaction surface designs has been investigated. Experimental results show that the time-varying collection efficiency depends on the surface coating condition, thickness of particle deposit, and impaction surface design. Deposited particles change the surface condition such that the particle collection efficiency decreases with time for the coated impaction surface while it increases with time for the uncoated impaction surface. However, after heavy loading, the collection efficiency eventually approaches nearly the same asymptotic value whether the impaction surface is coated or not. The impaction surface with an inverted conical cavity and an orifice plate alleviates particle bounce and reentrainment problems during particle collection process, resulting in a much greater collection efficiency than the conventional design, which uses flat impaction surface.