Abstract: Rice is a very responsive crop to nitrogen, but the efficiency of the N-fertilizers is low. Greenhouse experiment has been conducted to evaluate some synthetic (N-serve) and natural (neem cake and waste tea) nitrification inhibitors to improve fertilizer efficiency and reduce N-losses in rice fields. Nitrogen was applied as urea and ammonium sulfate at a rate of 60 mg/Kg soil. Results revealed that addition of inhibitors with both N fertilizer caused a significantly increase in both grain and straw yields rice, addition of 0.04 percent neem cake with both urea and as gave the highest grain and straw yields of rice while the waste tea gave the lowest. The percentage increase of total yield with urea + inhibitor treatments ranged between 5.8 percent to 26 percent when compared with urea alone, 26 percent increase was recorded for 0.04 percent neem cake treatment and 22.4 percent for N-serve, while 5.8 percent was recorded for 0.04 percent waste tea treatment, Also, the percentage increase in total rice yield over AS alone was 14.4 percent and 25.6 percent for 0.02 percent and 0.04 percent neem cake treatments respectively, while was 8.8 percent for N-serve treatment. Results also showed that neem cake combined with both urea and AS was more effectiveness on N-uptake especially at applied rate (0.04 percent). The percentage increase in total N-uptake over urea alone was 31 percent , 29 percent and 5 percent for 0.04 percent neem cake, N-serve and 0.04 percent waste tea respectively. On the other hand, the percentage increase of total N-uptake over all as alone was 29 percent and 15 percent for 0.04 percent and 0.02 percent neem cake treatments respectively, while, the waste tea a very low increase in total N-uptake. N-recovery by rice plant increased from 285 to 513 mg N/pot as a result of addition of inhibitors, as well as an improved in the utilization efficiency of N from urea and AS fertilizers was recorded.