Abstract: Hydroponically grown long-mat rice seedlings (HLMS) is a novel seedling cultivation method that improves work efficiency with lower labor costs, increases flexibility of seedling age, enables high-yield and high-efficiency rice production. Seedbed nutrient management is very important for the cultivation of vigorous rice seedlings under mechanical transplanting. Thus, it is of great importance for high yield formation to understand rice seedling quality, mechanical transplanting quality, field growth characteristics and yield formation affected by different nutrient solution concentrations. In this paper, field experiment was conducted in 2014 by using two different cultivars japonica rice (Wuyunjing 24) and indica hybrid rice (6 Liangyou 9368) under different nutrient solution concentrations S1, S2, S4 and S8 for HLMS. Those treatments mean 1, 2, 4, 8 times as much as original nutrient solution concentration, respectively, and the composition of original nutrients in the solution were 0.643 g/kg N, 0.615 g/kg P2O5, 0.359 g/kg K2O, 127.2 mg/kg Mg, 26.34 mg/kg Fe, 8.26 mg/kg Mn, 0.11 mg/kg Mo, 0.66 mg/kg B, 0.99 mg/kg Zn, 1.405 mg/kg Cu, 49 mg/kg SiO2, 709.1 mg/kg Ca. The results showed that there were increases in shoot dry biomass, seedling base stem diameter, root-developing ability, plant nitrogen content, leaf area index and photosynthetic rate along with the increase of nutrient solution concentrations for both cultivars before transplantation. However, under the high nutrient solution concentration (S8), the root growth (dry matter accumulation, root activity) was inhibited, seedling emergence rate and antioxidant enzymes activities (superoxide dismutase (SOD), peroxidase (POD)), malonaldehyde (MDA) contents in leaves and roots were decreased. Further, the missing hill rate was increased along with the increase of nutrient solution concentrations in both Wuyunjing 24 and 6 Liangyou 9368 cultivars, and it was significantly higher in S8 than that of S1, S2 and S4. The floating seedling rate was increased firstly and then decreased with the increase of nutrient solution concentrations. The differences of seedlings per hill among all treatments were not obvious for Wuyunjing 24, but the seedlings per hill of S1, S2, S4 treatments were respectively significantly higher than that of S8(P?0.05) for 6 Liangyou 9368. There was no significant difference in dry matter accumulation among treatments S2, S4 and S8 at maturity stage of Wuyunjing 24.; but for 6 Liangyou 9368, the dry matter accumulation at maturity of treatment S2 and S4 were significantly higher than that of treatment S1 and S8 , respectively. The period dry matter accumulation ratio from heading to maturity stage was increased firstly and then decreased with the increase of nutrient solution concentrations. The reduction of grain yield under treatment S1 (10.74 t/hm2 for Wuyunjing 24 and 10.96 t/hm2 for 6 Liangyou 9368) resulted from weaker seedling quality, slower seedling reviving in the paddy field, delayed tiller emergence, lower dry matter accumulation in the paddy field and less panicles. Under the treatment S2 and S4, the grain yield of Wuyunjing 24 was 12.09 and 11.64 t/hm2 respectively, and 6 Liangyou 9368 were 12.16 and 12.47 t/hm2. The grain yield increased with the increase of nutrient solution concentrations when the concentration of nutrient solution was equal or less than 4 times of the original solution. However, the grain yield did not continue to increase with the increase of nutrient solution concentration due to the non-increased panicles and the decreased spikelets number per panicle. The grain yield of Wuyunjing 24 and 6 Liangyou 9368 were 11.59 and 11.48 t/hm2 under S8 treatment). Therefore, the suitable nutrient solution concentration of HLMS was S2 for Wuyunjing 24 and S2-S4 for 6 Liangyou 9368.