The effect of concentration and time of supplementary nitrogen fertilizer spray application on grain yield and nitrogen use efficiency in rapeseed (Hyola401) as a second crop in paddy fields were evaluated in a field experiment conducted in randomized complete block design with 3 replications at Rice Research Institute of Iran (Rasht) in 2008. In this experiment two factors, concentration of solution containing nitrogen fertilizer (urea) at two levels (5 and 100.00) and application time in seven levels: 1-seedling stage at 6-8 leaves (1.06-1.08 Sylvester-Bradley and Makepeace coding system), 2: beginning of stem elongation (2.01-2.03), 3: pre-flowering (3.9), 4: 1.06-1.08 + 2.01-2.03, 5: 1.06- 1.08 + 3.9, 6: 2.01-2.03 + 3.9, 7: 1.06-1.08 + 2.01- 2.03 + 3.9, plus two control treatments a: zero nitrogen fertilizer b: conventional fertilization (180 kg.ha-1) at seed sowing, stem elongation and prior to flowering in equal rates. Plant characteristics (grain yield and oil content) were measured and nitrogen agronomic efficiency (NAE), nitrogen use efficiency (NUE), nitrogen apparent recovery fraction (NRF), nitrogen physiological efficiency (NPE), nitrogen harvest index (NHI), nitrogen uptake efficiency (UPE) and nitrogen utilization efficiency (UTE) were calculated. Results showed a significant difference between concentration and times of nitrogen spray application effect on grain yield, agronomic efficiency, and harvest index of nitrogen. Spray application of nitrogen (100.00) in 2.01- 2.03+3.9 stages (Treatment #6) produced the maximum grain yield (4221.7 kg.ha-1), agronomic efficiency (17.94 kg.kg-1), use efficiency (23.45 kg.kg-1) and harvest index (77.39%) of nitrogen. Spray application of nitrogen (100.00) at all growth stages produced the maximum Apparent recovery Fraction and uptake efficiency (70.71% and 87.12 kg.kg-1, respectively) of nitrogen. According to the results of the present experiment, it seems the spray application of supplementary nitrogen fertilizer at beginning of stem elongation and prior to flowering stages, may help to provide fertilizer needs and help to nitrogen fertilizer use efficiency and grain yield enhancement.