Microfiltration (MF) does not remove color, natural organic matter (NOM) or synthetic organic chemicals (SOCs). It must be combined with other conventional technologies such as activated carbon adsorption to overcome some of these limitations. The effects of granular activated carbon (GAC) addition on MF performance in terms of quality (dissolved organic carbon) and quantity (permeate flux) were investigated. For a water purification experiment, MF showed preferential rejection of UV260 (about 30%) compared to dissolved organic carbon (DOC) (about 10%), indicating that the hydrophobic (aromatic) NOM fraction is more efficiently eliminated. In the hybrid MF membrane system, the removal efficiency of UV260 was about 60% compared to 30% by MF alone, and the decreasing rate of membrane permeability was much less than that of a conventional MF membrane process (about 70 days without GAC and 130 days with GAC). This may result from the reduced organic loading to the membrane due to the adsorption of NOM on the GAC. Using MF alone, the average removal efficiency of specific UV absorbance (SUVA, UV260/DOC) was only 20%, but GAC addition increased SUVA removal efficiency up to 50-60%. In conclusion, the addition of GAC resulted in a decrease of hydrophobic NOM and trihalomethane precursors. For the wastewater reclamation/reuse experiment, removal efficiencies of DOC, chemical oxygen demand, total nitrogen, total phosphorus and turbidity were in the range of 42%, 53%, 15%, 13%, and 100% with the MF-GAC hybrid membrane system whereas 25-30%, 20-25%, 5-10%, 5-8% and 100% with the MF membrane alone, respectively. The hybrid process of membrane filtration and GAC was more effective in treatment efficiency than the single process.