Moisture content of composite pregregs are known to significantly affect the process-induced laminate microstructure and formation of microvoids during cure. After the composite laminate is cured, these microvoids often act as storage sites for the diffused moisture and may further lead to considerable reduction of mechanical properties of the laminate. In this study, the moisture absorption of eight-ply Quartz (AQ 581)/Bismaleimide (BMI) composite laminates is investigated. Four different types of composite laminates are fabricated using eight plies which were preconditioned at 2%, 40%, 70% or 99% relative humidity before curing. Two different sample sizes of 31.75 × 31.75 mm and 57.15 × 12.7 mm are cut from each laminate and subsequently immersed into distilled water at 25℃. Experimental weight gain data for each sample are obtained by periodically weighing all samples over a period of 9 months. The non-Fickian absorption dynamics observed in weight gain data is modelled by the three-dimensional, anisotropic, hindered diffusion model (HDM). The hindered diffusion model is shown to accurately predict both short-term Fickian and long-term anomalous moisture absorption behavior of all composite samples. An increase in both maximum possible moisture absorption and degree of anomalous behavior is observed for the composite samples as the relative humidity of prepreg preconditioning is increased up to 70%. Further increase of preconditioning humidity from 70% to 99% does not have a significant effect on the moisture absorption of samples. The content of the microvoids in each laminate are observed to correlate well with increasing maximum moisture content and the extent of non-Fickian behavior. The effects of diffusion hindrance due to storage of prepregs in humid environments are illustrated by the two-dimensional, through-the-thickness moisture concentration profiles. Keywords: Moisture Absorption, Preconditioning, Composites, Concentration Profiles, Hindrance Effects.