Effect of humic acid (HA) with periodic nitrogen back-flushing was investigated in hybrid process of alumina microfiltration and photocatalyst for drinking water treatment. It was compared and investigated with the previous results of microfiltration water back-flushing or ultrafiltration nitrogen back-flushing in viewpoints of membrane fouling resistance ($R_f$), permeate flux (J), and total permeate volume ($V_T$). As results, the trends of membrane fouling were different depending on nitrogen or water back-flushing, and depending on ultrafiltration or microfiltration made with the same material. Also, the nitrogen back-flushing using microfiltration was more effective membrane fouling inhibition than ultrafiltration, and the nitrogen back-flushing was more effective than water back-flushing using the same microfiltration membrane. Turbidity treatment efficiencies were almost constant independent of HA concentration, but HA treatment efficiency was the maximum at HA 10 mg/L. From this results, it was shown that the treated water HA quality increased as increasing HA concentration, but HA could be removed the most effectively by photocatalyst beads adsorption and photo-oxidation at HA 10 mg/L.