The enhancement of dielectric constant (K) in humid atmosphere (K-max = 13360 in dry atmosphere to 17450 in 100% relative humidity) for lead magnesium niobate [Pb(Mg1/3Nb2/3)O-3] relaxor materials sintered at 950 degrees C for 30 min (using 3 wt% excess Pbo as a sintering aid) can be explained by the extended low frequency dispersion (LFD) model proposed earlier. However, it has been observed that for samples containing excess MgO, such enhancement of K-max in humid atmosphere is not so remarkable. It has been shown that in case of samples containing excess MgO, owing to the presence of already formed OH- ions at the surface arising out of the reaction of adsorbed moisture with MgO, the physical absorption of polar H2O molecules in humid atmosphere will be much less and consequently the enhancement of dielectric response in humid atmosphere should be low.