Eggs, nymphs, and adults of Halyomorpha halys were exposed to 15%, 35%, 55%, 75%, or 90% RH provided by glycerol-water solutions. Although egg hatch and nymphal survival occurred at all concentrations, they were highest at 55% to 90% RH. Nymphs exposed at the second instar reached the adult stage only at 55% to 90% RH. Females laid the greatest number of egg clutches at 55% RH. Therefore, we believe that H. halys could survive in Florida at 55% to 90% RH, but would be most prolific at 55%.