Characteristics and oxidizing ability of both $NH_4-N$ and$NO^2$-N were examined for the strains isolated from wastewater treatment facilities and from natural systems by using Winogradsky columns. In case of $NH_4$-N, the most efficient strain was Nitrosomonas KB1 isolated from wastewater treatment facility of K corporation and in case of $NO_2$-N, it was Nitrobacter KB2 from the same site as Nitrosomonas KB1. For Nitrosomonas KB1, 91% of $NH_4$-N was oxidized after 4 days of cultivation. Optimal growth temperature and initial pH of Nitrosomonas KB1 were $28^{circ}C$ and 7, respectively. In comparison to oxidizing rates with changing initial concentration of $NH_4$-N, the ammonia oxidizing rate was increased up to 6.7 mg/day for the initial $NO_2$-N concentrations for the region lower than 100 mg $NH_4-N/L$, but it was gradually reduced for the region higher than 100 mg $NH_4-N/L$. For Nitrobacter KB2 90% of $NO_2$-N was removed after culturing for 4 days. Optimal growth temperature and initial pH of Nitrobacter KB2 was $28^{circ}C$ and 7, respectively. And the nitrite oxidizing rate was increased in proportion to the initial concentrations of $NO_2$-N up to 200 mg/$ell$, and it was maintained almost 4.2 mg/day irrespective of initial $NO_2$-N higher than 200 mg/L.