The Gongji stream water of Chuncheon city was filtrated by 2 kinds of tubular alumina ceramic MF membranes with periodic $N_2$-back-flushing. $N_2$-back-flushing time (BT) was changed in $0{sim}50$ sec at fixed filtration time (FT), or back-flushing period, of 4 min for NCMT-5231 membrane ($0.05;{mu}m$). Then, FT was changed in $0{sim}32$ min at fixed BT of 40 sec for NCMT-7231 $0.1{mu}m)$). In the viewpoints of total permeate volume ($V_T$), dimensionless permeate flux ($J/J_0$) and resistance of membrane fouling ($R_f$), the optimal $N_2$-BT was 50 sec, which was the longest BT, at 4 min FT for NCMT-5231. It means the longest BT was the most effective to minimize the membrane fouling, and we could acquire the most $V_T$. But the optimal FT for NCMT-7231 was 16 min in the viewpoint of $V_T$, and was 8 min in the viewpoints of $J/J_0$ and $R_f$ at fixed BT of 40 sec. The rejection rates were excellent as $80.6{sim}96.6;%$ for turbidity, $35.2{sim}58.4%$ for $NH_3$-N, $16.3{sim}45.2%$ for T-P and $16.3{sim}45.2%$ for $COD_{Mn}$. However, the rejection rate of T-N was very low as $2.7{sim}13.4%$ and it of TDS below 6.1%.