To investigate physiological characteristics of Saccharina japonica cultured in enriched media with different nitrogen sources, kelp were cultured for 7 days in three nitrogen conditions, including natural seawater, enrichment of ammonia and nitrate, and then growth rate, photosynthesis at different carbon levels (P-Ci curve) and nitrogen uptake rate were determined, respectively. The results showed that both enrichments of ammonia and nitrate remarkably enhanced growth of kelp, but no significant difference between the two treatments. P-Ci curve conformed to the saturated kinetics equation, and both the maximal photosynthetic rate (V_max) and half saturated constant (K_s) were notably raised by enriched nitrogen. However, V_max showed no significant difference between the two nitrogen enrichment, while K_s exhibited a higher value in ammonia than in nitrate enrichment. Compared to natural seawater, the ratio of V_max/K_s increased in enrichment of nitrate and kept no change in enrichment of ammonia. Contents of Chl.α and Car were enhanced by enrichment of nitrogen, with no significant difference between the two nitrogen sources enrichments. Content of soluble sugar was decreased by enriched nitrogen, and showed a lower value in enrichment of ammonia than nitrate. Compared with natural seawater, ammonia enrichment enhanced ammonia uptake and inhibited nitrate uptake, while enrichment of nitrate increased nitrate uptake and had no remarkable effect on ammonia uptake. In conclusion, enrichments with both two nitrogen sources could enhance uptake of carbon and nitrogen, but ammonia enrichment had advantage in nitrogen uptake, while nitrate enrichment showed more remarkable influence on carbon fixation. Therefore, the balance of carbon and nitrogen utilization affected by enrichment of ammonia or nitrate resulted in no significant difference in growth rate between the two treatments.