This experiment was carried out to determine the effect of improvement of oversown pastures, treated with four nitrogen(N) application levels(0, 100, 200, 300 kg/ha) and three species mixtures (A: orchardgrass+ladino clover; B: orchardgrass+ladino clover+perennial ryegrass; C: orchardgrass+ladino clover+perennial ryegrass+Italian ryegrass). The establishment of perennial ryegrass, Italian ryegrass, and ladino clover were increased with increased N applications, but the ryegrass mixed with orchardgrass and ladino clover decreased the establishment of ladino clover. With the increase of N application levels, orchardgrass, perennial ryegrass and Italian ryegrass in comparison on botanical composition were getting better, while the native plants established already were decreased. The botanical composition of newly sown pasture plants was increased as cutting times progressed. The dry matter(DM) yield of pasture species increased significantly with N application up to 300 kg/ha. There was no significance among mixture treatments, although the DM yield of basic treatment(orchardgrass+ladino clover) was higher than other treatments. However, when compared DM yields on each cutting times, newly oversown pastures in A treatment was shown to be significantly higher only on 2nd cutting time than other treatments(P<0.05). The DM yield of native plants survived in basic species mixture was significantly less than those of other mixtures(P<0.05). Results of this study indicate that for improving oversown pastures, at least 300 kg/ha N application should be applied, and basic mixture (orchardgrass+ladino clover) has more advantage than treatments mixed with ryegrass.