Abstract: The effect of a combination of inorganic fertilizer and organic inputs on nitrogen uptake and utilization efficiency was compared with that of only inorganic fertilizer. The treatments involved the addition of equivalent amounts of N (80 kg N ha-1) through inorganic fertilizer or three organic inputs (rice straw, rice root, or rice hull), in addition to a control treatment for rice (Oryza sativa L.) cultivars Koshihikari and Sakha 102. Rice straw was applied at two rates that corresponded to 5 and 10 Mg ha-1, the application rate of rice hull was 5 Mg ha-1 and rice root was 2.5 Mg ha-1. The rates of N utilization efficiency after 100th days after transplanting with 5 Mg ha-1 rice straw were relatively higher and ranged from 18.5 to 20.5%, while that with 10 Mg ha-1 ranged from 14.6 to 15.6%. The results show that a combination of inorganic fertilizers and rice straw enhanced N utilization efficiency. It is suggested that rice straw integrated with 40 kg N ha-1 of inorganic fertilizers and applied at a suitable time had a positive effect on N uptake derived from rice straw, whereas higher rates of rice straw application had an adverse affect on N uptake by the rice crop.